CBSE Class 10 Science — Long Answer Questions

(a) Given below are certain situations. Analyse each and describe its possible impact: (i) A population of bacteria living in temperate waters whose temperature increased by global warming. (ii) The sperm encounters the egg when it reaches the oviduct in human females. (iii) Self pollination does not occur in a flower that contains only pistil. (iv) Egg does not get fertilised in a human female. (v) When the seed is placed under appropriate condition of water and air in the soil? OR (b) Given below are certain situations. Analyse and describe what would happen when: (i) Spores are liberated from blob-like structures of the bread mould? (ii) Leaves of bryophyllum fall on wet soil? (iii) A pollen from different species land on the stigma of totally unrelated species? (iv) Copper-T is placed in the uterus of a human female? (v) Spirogyra breaks into smaller fragments upon maturation?

(a) (i) Give reasons for the following: (I) Covalent compounds are poor conductor of electricity. (II) Soap does not form lather in hard water. (III) Carbon shows catenation but silicon does not. (ii) Write chemical equations for the following: (I) Oxidation of ethanol by acidified $\mathrm{K}_2\mathrm{Cr}_2\mathrm{O}_7$ (II) Hydrogenation of ethene. OR (b) Mohan heated ethanol with a compound 'X' in the presence of a few drops of conc. $\mathrm{H}_2\mathrm{SO}_4$ and observed a sweet smelling compound 'Y' is formed. When 'Y' is treated with sodium hydroxide it gives back ethanol and a compound 'Z'. (i) Identify 'X', 'Y' and 'Z'. (ii) Write the role of conc. $\mathrm{H}_2\mathrm{SO}_4$ in the reaction. (iii) Write the chemical equations involved and name the reactions.

(A) (i) State the rule which gives the direction of force acting on the current carrying conductor placed in a uniform magnetic field. (ii) Name any two devices which work on the basis of an interaction between magnetic field and current carrying conductor. (iii) Comment on the magnitude of force on electron in both the cases and give reason for your answer. OR (B) (i) List three possible reasons of short-circuiting in an electric circuit. (ii) In case of overload, will the fuse protect to given electric circuit from damage? Justify your answer. (iii) For an electric heater rated as 220 V, 2200 W, what should be the minimum rating of fuse used with it?

(A) (i) Give reasons for the following: (I) Ionic compound have generally high melting points and boiling points. (II) Solder, an alloy of lead and tin, is used for welding electrical wires. (III) Carbon cannot reduce the oxides of Na or Mg. (ii) The reaction of compound 'X' with aluminium is used to join railway tracks: (I) Identify the compound 'X'. (II) Name the reaction. (III) Write the balanced chemical equation of the reaction of compound 'X' with aluminium. OR (B) (i) Write the balanced chemical equations when: (I) A mixture of $Cu_2O$ and $Cu_2S$ is heated. (II) $ZnS$ is heated in the presence of oxygen. (ii) Give reasons for the following: (I) The wires carrying current in homes have a coating of PVC. (II) To make hot water tanks, copper is used and not steel. (iii) Show the formation of ionic compound $CaO$ with electron dot structure. [Atomic number: $Ca = 20, O = 8$]

(A) (i) Sugarcane does not produce seeds so name the process through which it will be able to reproduce. (ii) List any two advantages of this method. (iii) Besides sugarcane, give two more examples of plants that reproduce by this method. (iv) Why regeneration is not possible in all the types of animals? OR (B) (i) In an angiospermic flower, fertilization is said to take place when male gametes carried in the pollen tube fuse with the female gamete, present in the embryo sac. This results in lot of changes in different parts of the flower. State the changes taking place in the following structures of flower post fertilization: (a) Zygote (b) Ovule (c) Ovary (d) Sepals (ii) Define germination.

Attempt either option (A) or (B): (A) (i) Give reasons for the following: (I) Ionic compounds have generally high melting points and boiling points. (II) Solder, an alloy of lead and tin, is used for welding electrical wires. (III) Carbon cannot reduce the oxides of Na or Mg. (ii) The reaction of compound 'X' with aluminium is used to join railway tracks: (I) Identify the compound 'X'. (II) Name the reaction. (III) Write the balanced chemical equation of the reaction of compound 'X' with aluminium. [3+2] OR (B) (i) Write the balanced chemical equations when: (I) A mixture of $Cu_2O$ and $Cu_2S$ is heated. (II) $ZnS$ is heated in the presence of oxygen. (ii) Give reasons for the following: (I) The wires carrying current in homes have a coating of PVC. (II) To make hot water tanks, copper is used and not steel. (iii) Show the formation of ionic compound $CaO$ with electron dot structure. [Atomic number: $Ca = 20$, $O = 8$] [2+2+1]

(A) (i) List any two features of the electric current used in the houses of India. (ii) Write any two differences between direct current and alternating current. (iii) How will you identify the live wire and the neutral wire in a domestic electric circuit? OR (B) (i) Why is fuse an important component in our electric circuits? (ii) Distinguish between overloading and short-circuiting of a circuit. (iii) Giving reason, explain what type of materials are used in fuse wires.

(a) Name an alcohol and a carboxylic acid having two carbon atoms in their structures. Draw their structures and state how this alcohol can be converted into a carboxylic acid. What happens when these two compounds react in the presence of an acid? Write chemical equations for the reactions involved in the two cases mentioned above. OR (b) What are soaps? Write the structure of a soap molecule. Explain the cleansing action of a soap. Why are soaps not considered suitable for washing clothes in a region where water is hard? How is this problem overcomed?

(a) Define Puberty. List any two changes seen in boys at the time of puberty. (b) Why are testes in human males located outside the abdominal cavity in scrotum? (c) List any three techniques of contraception used by humans. Which one of these is not meant for males? OR (a) Name the part performing following functions in human female reproductive system: (i) production of eggs (ii) site of fertilization (iii) site of implantation (iv) entry of the sperms (b) What changes are observed in the uterus: (i) subsequent to implantation of zygote and (ii) if an egg does not get fertilized?

(a) What are magnetic field lines? How is the direction of magnetic field at a point determined? Draw the pattern of magnetic field lines of the magnetic field produced by a current carrying circular loop. Mark on it the direction of (i) current and (ii) magnetic field lines. Name the two factors on which the magnitude of the magnetic field due to a current carrying coil depends. OR (b) Why can't two magnetic field lines cross each other? Draw magnetic field lines showing the direction of the magnetic field due to a current carrying long straight solenoid. State the conclusion which can be drawn from the pattern of magnetic field lines inside the solenoid. Name any two factors on which the magnitude of the magnetic field due to this solenoid depends.

(A) (a) What is meant by the term homologous series of carbon compounds? Write molecular formula of any two consecutive members of homologous series of ketones. (b) Write chemical equation of the reactions of ethanoic acid with (i) Sodium hydroxide and (ii) Ethanol (in the presence of an acid); giving the name of the products in each case. (c) Draw the structure of the molecule of benzene. OR (B) (a) Write the molecular formula of ethyne and draw its electron dot structure. (b) Write chemical equation to show the reaction of ethanol with (i) Sodium metal (ii) Ethanoic acid (in the presence of an acid) (iii) Acidified potassium dichromate Write the name of the product formed in each case.

(A) (a) Observe the following diagram and compare (i) speed of light and (ii) optical densities of the three media A, B and C. Also give justification for your answer of any one of the two cases in terms of refractive indices of A, B and C. (b) Redraw the path of a ray of light through the three media, if the ray of light starting from medium A falls on the medium B (i) Obliquely and the optical density of medium B is made more than that of A and C. (ii) The ray falls normally from medium A to medium B. OR (B) Analyse the following observation table showing variation of image distance (v) with object distance (u) in case of a convex lens and answer the questions that follow without doing any calculations: | Observation Number | Object distance (u) in cm | Image distance (v) in cm | |---|---|---| | 1 | -15 | -60 | | 2 | -25 | +100 | | 3 | -30 | +60 | | 4 | -40 | +40 | | 5 | -60 | +30 | | 6 | -100 | +25 | (a) Determine the focal length of the lens. Give reason for your answer. (b) Find magnification of the image formed in Observation No. 3. (c) The numerical value of magnifications in cases of observation 1 and 2 is same. List two differences in the images formed in these two cases.

(A) (a) Analyse the given situations and interpret the possible reason for each: (i) Iodine deficiency in diet increases the possibility of a disease of swollen neck in a person. (ii) Some people in population may have very short heights (dwarfs). (iii) Thick facial hairs develop in boys at the age of 10-12 years. (b) Explain two reasons which necessitate the need of chemical communication in multicellular organisms. OR (B) (a) Differentiate between voluntary and involuntary action. (b) Define reflex action. With the help of a flow diagram, show the correct sequence of path of Nerve impulse from place of its origin.

(A) (i) Draw the pattern of the magnetic field lines for the two parallel straight conductors carrying current of same magnitude 'I' in opposite directions as shown. Show the direction of magnetic field at a point O which is equidistant from the two conductors. (Consider that the conductors are inserted normal to the plane of a rectangular cardboard.) (ii) In our houses we receive A.C. electric power of $220\text{ V}$. In electric iron or electric heater cables having three wires with insulation of three different colours - red, black and green are used to draw current from the mains. (a) What are these three different wires called? Name them colourwise. (b) What is the potential difference between the red wire and the black wire? (c) What is the role of the wire with green insulation in case of accidental leakage of electric current to the metallic body of an electrical appliance? OR (B) (i) By using the given experimental set-up. How can it be shown that: (a) a force is exerted on the current-carrying conductor AB when it is placed in a magnetic field. (b) the direction of force can be reversed in two ways. (ii) When will the magnitude of the force be highest? (iii) State Fleming's left hand rule.

(A) (i) What is regeneration? Give one example of an organism that shows this process and one organism that does not. Why does regeneration not occur in the latter? (ii) Water in a pond appears dark green and contains filamentous structures. Name these structures and the method by which they reproduce. Explain the process. OR (B) (i) Name the part performing following functions in human male reproductive system: (a) Carries sperm (b) Production of male gametes (c) Whose secretion makes the transport of sperms easier (d) Provide suitable temperature for sperm formation (ii) Write any two characteristics of sperms. (iii) What are surgical contraceptive methods? Give the side effect caused by this procedure.

(A) A carbon compound 'A' on heating with excess conc. $H_2SO_4$ forms a compound 'B', which on addition of one mole of hydrogen gas in the presence of nickel catalyst forms a compound 'C'. 'C' on combustion in air forms 2 moles of carbon dioxide and 3 moles of water. Identify 'A', 'B' and 'C' and write their structures. Give chemical equations of the reactions involved. Also state the role of concentrated sulphuric acid in the formation of 'B' from 'A'. OR (B) A carbon compound 'A' is widely used as a preservative in pickles and has a molecular formula $C_2H_4O_2$. This compound reacts with ethanol to form a sweet smelling compound 'B'. (i) Identify the compound 'A' and write its structure. (ii) Write the chemical equation for the reaction of 'A' with ethanol to form compound 'B'. State the role of presence of an acid in the reaction. (iii) How can we get compound 'A' back from 'B'? (iv) How can 'A' be obtained from ethanol? (v) Name the gas produced when compound 'A' reacts with washing soda.

(a) (i) "In refraction of light through a rectangular glass slab, the emergent ray is always parallel to the direction of the incident ray." Why? Explain with the help of a ray diagram. What happens when a ray of light falls normally on one of the faces of a rectangular glass prism? Draw diagram. (ii) An object is placed at a distance of $30\ \mathrm{cm}$ from the optical centre of a concave lens of focal length $20\ \mathrm{cm}$. Use Lens formula to determine the position of the image formed in this case. OR (b) (i) A student wishes to study the image formation by a concave mirror using candle flame as object. State the type of the image formed by the mirror and mention the change in the image formed, if any, that he observes when the candle flame is gradually moved away from the pole of the mirror. Draw a ray diagram to show the image formation when the object distance is nearly equal to the radius of curvature of the mirror. (ii) A convex mirror used for rear-view on an automobile has a focal length of $3\cdot 0\ \mathrm{m}$. If a bus is located at $6\cdot 0\ \mathrm{m}$ from this mirror, use mirror formula to find the position of the image of the bus as seen in the mirror.

(a) (i) Identify the parts 'X' and 'Y' in the figure given below : (ii) Name the yellowish coloured structures produced by the part labelled as 'Y'. (iii) Write the name of the process by which these are transferred to the part labelled as 'X'. (iv) Explain the process of seed formation in a flowering plant. OR (b) (i) Name the type of asexual mode of reproduction shown in the given figure. (ii) Identify the unicellular organism in the diagram. (iii) List any two advantages of asexual reproduction over sexual reproduction. (iv) Name and explain any one mode of asexual reproduction observed in Hydra.

(a) (i) Consider the following metals: K, Ca, Al, Cu, Ag, Fe Select from the above metals, a metal which I. does not react with oxygen even at high temperature. II. reacts with oxygen at ordinary temperature and forms a protective oxide layer which prevents the metal from further oxidation. III. catches fire when kept in the open. IV. does not burn in oxygen but the hot metal is coated with a black coloured oxide layer. (ii) What are amphoteric oxides? With the help of balanced chemical equations show that aluminium oxide is an amphoteric oxide. (iii) What are alkalis? Give one example. OR (b) (i) With the help of balanced chemical equations state the process of extracting (I) mercury from its ore called cinnabar, and (II) copper from its sulphide ore. (ii) Silver and copper articles slowly lose their shiny surfaces when exposed to air. Name the compounds formed on (I) silver articles, and (II) copper articles in the form of coating.

(a) The given figure shows the current passing through the straight conductor XY. (i) Copy the diagram and draw the magnetic field lines when current flows from conductor X to Y. (ii) Name and state the rule used in determining the direction of the magnetic field lines in the situation given above. (iii) State Fleming's left hand rule. Using this rule, determine the direction of force applied on an electron entering a uniform magnetic field as shown in the figure. OR (b) (i) Define the term solenoid. Draw the pattern of the magnetic field lines in and around a current carrying straight solenoid. Mark on the pattern the (i) direction of current, (ii) direction of field lines near the ends of the solenoid, and (iii) region where the magnetic field is uniform. (ii) How would you make an electromagnet using a current carrying solenoid?

(a) (i) "The length of the small intestine in various animals depends on the food they eat." Justify the statement. (ii) Discuss the role of the pancreas and bile juice in the digestion of food in human beings. (iii) How is the small intestine designed to absorb digested food? OR (b) (i) State the role of rings of cartilage present in the throat. (ii) Discuss the role of the ribs and diaphragm when air is taken in during the breathing cycle. (iii) Why do we get muscle cramps during heavy exercise? Explain.

(a) (i) A compound 'X' having two carbon atoms in its molecule turns blue litmus red and $5-8\%$ solution of 'X' in water is widely used as a preservative. Identify the compound 'X' and write its structure. (ii) Compare its pH nature with a mineral acid. (iii) 'X' on reacting with alcohols produces sweet smelling compounds, used in making perfumes. Name the reaction and write its chemical equation. (iv) When sodium carbonate is added to 'X', a colourless gas is produced which turns lime water milky. Write the chemical equation for the reaction giving the name of the salt produced. OR (b) (i) Differentiate between saturated and unsaturated hydrocarbons by giving one example each, with a structural formula. (ii) Write the method of converting an unsaturated hydrocarbon into a saturated hydrocarbon. Name the industry where this reaction is commonly used. (iii) Write the name and structure of a hydrocarbon having double bond and four carbon atoms in its one molecule.

(a) (i) The power of a lens 'X' is $-2.5\ D$. Name the lens and determine its focal length in cm. For which eye defect of vision will an optician prescribe this type of lens as a corrective lens? (ii) "The value of magnification 'm' for a lens is $-2$." Using new Cartesian Sign Convention and considering that an object is placed at a distance of $20\ cm$ from the optical centre of this lens, state : (I) the nature of the image formed; (II) size of the image compared to the size of the object; (III) position of the image, and (IV) sign of the height of the image. (iii) The numerical values of the focal lengths of two lenses A and B are $10\ cm$ and $20\ cm$ respectively. Which one of the two will show higher degree of convergence/divergence? Give reason to justify your answer. OR (b) (i) Draw a ray diagram to show the refraction of a ray of light through a rectangular glass slab when it falls obliquely from air into glass. (ii) State Snell's law of refraction of light. (iii) Differentiate between the virtual images formed by a convex lens and a concave lens on the basis of : (I) object distance, and (II) magnification.

(a) (i) Write the functions of the following parts of human female reproductive system : (I) Ovary (II) Fallopian tube (III) Uterus (ii) State briefly two contraceptive methods used by human males. OR (b) (i) Differentiate between self-pollination and cross-pollination. (ii) Identify A, B and C in the diagram given below and write one function of each.

(a) (i) Draw two isomeric structures of Butene $(C_4H_8)$. (ii) Name the following compounds (structural formulas of chloropropane isomers given). (iii) Write the chemical equations for the following reactions. Mention one essential condition each for these reactions to take place. (I) Ethanol undergoes complete oxidation (II) Propene undergoes hydrogenation (III) Ethanoic acid reacts with ethanol OR (b) (i) A carbon compound X is a good solvent. On reaction with sodium, X forms two products Y and Z. Z is used to convert vegetable oil into vegetable ghee. Identify and name X, Y and Z. Also write the equation of reaction of X with sodium to justify your answer. (ii) Write chemical equation to show what happens when ethanol : (I) burns in oxygen/air. (II) is heated at $443\ K$ in excess conc. $H_2SO_4$. (III) reacts with acidified potassium dichromate.

(a) A few crystals of ferrous sulphate were taken in a dry boiling tube and heated. Tiny water droplets were observed in the tube after some time. (i) From where did these water droplets appear? Explain. (ii) What colour change will be observed during heating? (iii) How many molecules of water are attached per molecule of $\mathrm{FeSO_4}$ crystal? Write the molecular formula of crystalline forms of (I) Copper sulphate, and (II) Sodium carbonate. (iv) State how is Plaster of Paris obtained from gypsum. Write two uses of Plaster of Paris. OR (b) An acid 'X' present in tamarind when mixed with 'Y', produces a mixture 'Z'. 'Z' on addition to a dough when heated makes cakes soft and spongy. 'Y' is prepared from common salt and helps in faster cooking. (i) Write the common names of 'X', 'Y' and 'Z', and the chemical formula of 'Y'. (ii) How is 'Y' prepared and how does it help in making cakes soft and spongy? Illustrate the reaction with suitable chemical equation. (iii) Write the name and chemical formula of a mild base other than 'Y' used as an antacid.

(a) (i) The potential difference across the two ends of a circuit component is decreased to one-third of its initial value, while its resistance remains constant. What change will be observed in the current flowing through it? Name and state the law which helps us to answer this question. (ii) Draw a schematic diagram of a circuit consisting of a battery of four $1.5 \mathrm{~V}$ cells, a $5 \Omega$ resistor, a $10 \Omega$ resistor and a $15 \Omega$ resistor and a plug key, all connected in series. Now find (I) the electric current passing through the circuit, and (II) potential difference across the $10 \Omega$ resistor when the plug key is closed. OR (b) (i) When is the potential difference between two points said to be 1 volt? (ii) A copper wire has a diameter of $0.2 \mathrm{~mm}$ and resistivity of $1.6 \times 10^{-8} \Omega \mathrm{~m}$. What will be the length of this wire to make its resistance $14 \Omega$? How much does the resistance change, if the diameter of the wire is doubled?

(a) Design an experiment to demonstrate that carbon dioxide is essential for photosynthesis. Write the observation and conclusion of the experiment. OR In the experimental set- up shown above in diagram (I) atmospheric air is being passed into lime water with a syringe while in diagram (II) air is being exhaled into lime water. The time taken for the lime water to turn milky in both the test tubes is different. Give reason. (ii) Draw the diagram of an open stomatal pore and label (I) Guard cells, and (II) Chloroplast on it. Mention two functions performed by stomata.

(a) The variation of image distance (v) with object distance (u) for a convex lens is given in the following observation table. Analyse it and answer the questions that follow : | S. No. | Object distance (u) cm | Image distance (v) cm | |---|---|---| | 1 | -150 | +30 | | 2 | -75 | +37.5 | | 3 | -50 | +50 | | 4 | -37.5 | +75 | | 5 | -30 | +150 | | 6 | -15 | +37.5 | (i) Without calculation, find the focal length of the convex lens. Justify your answer. (ii) Which observation is not correct? Why? Draw ray diagram to find the position of the image formed for this position of the object. (iii) Find the approximate value of magnification for $\mathrm{u} = - 30 \mathrm{cm}$. OR (b) (i) Define principal axis of a lens. Draw a ray diagram to show what happens when a ray of light parallel to the principal axis of a concave lens passes through it. (ii) The focal length of a concave lens is $20 \mathrm{cm}$. At what distance from the lens should a $5 \mathrm{cm}$ tall object be placed so that its image is formed at a distance of $15 \mathrm{cm}$ from the lens? Also calculate the size of the image formed.

(a) (i) Define a reflex arc. Why have reflex arcs evolved in animals? Trace the sequence of events which occur, when you suddenly touch a hot object. (ii) Name the part of nervous system which helps in communication between the central nervous system and other parts of the body. What are the two components of this system? OR (b) (i) Leaves of 'chhui-mui' plant begin to fold up and droop in response to a stimulus. Name the stimulus and write the cause for such a rapid movement. Is there any growth involved in the movement? (ii) Define geotropism in plants. What is meant by positive and negative geotropism? Give one example of each type.

(a) What is a chemical reaction? Describe one activity each to show that a chemical change has occurred in which (i) change of colour, and (ii) change in temperature has taken place. OR (b) (i) Define a decomposition reaction. How can we say that (I) electrolysis of water, and (II) blackening of silver bromide when exposed to sunlight, are decomposition reactions? Mention the type of energy involved in each case. (ii) "The type of reactions in which (I) calcium oxide is formed, and (II) calcium hydroxide is formed are opposite reactions to each other." Justify this statement with the help of chemical equations.

(a) (i) Draw a ray diagram to show the path of the refracted ray in each of the following cases: A ray of light incident on a concave lens (1) parallel to its principal axis, and (2) is directed towards its principal focus. (ii) A 4 cm tall object is placed perpendicular to the principal axis of convex lens of focal length 24 cm. The distance of object from the lens is 16 cm. Find the position and size of image formed. OR (b) (i) Draw a ray diagram to show the path of the reflected ray in each of the following cases: A ray of light incident on a convex mirror (1) parallel to its principal axis, and (2) is directed towards its principal focus. (ii) A 1.5 cm tall candle flame is placed perpendicular to the principal axis of a concave mirror of focal length 12 cm. If the distance of the flame from the pole of the mirror is 18 cm, use mirror formula to determine the position and size of the image formed.

(a) (i) What are spores? On which structures are they formed? How do they overcome unfavourable conditions? Name the organism which multiplies with the help of these structures. (ii) Give two reasons why some plants are grown by the method of vegetative propagation. List two methods used to grow plants vegetatively. OR (b) (i) Study the diagram given below and name the parts marked as A, B and C. What happens when B reaches C in the ovary? Mention its significance. (ii) Write the post fertilisation changes that occur in a flower.

(a) (i) Five solutions A, B, C, D and E when tested with pH paper showed pH as 4, 1, 13, 7 and 10 respectively. Which solution is: (1) Strongly acidic (2) Strongly alkaline (3) Weakly acidic (4) Neutral and (5) Weakly alkaline? Arrange the solutions in increasing order of $H^+$ ion concentration. (ii) Write the name and formula of (1) an acidic salt and (2) a basic salt giving the name of the parent acid and parent base used to form the salt in each case. OR (b) Name and state in brief the process which is used to prepare sodium hydroxide from sodium chloride. In this process along with the main product two gases 'X' and 'Y' are also given off at the two electrodes. Name 'X' and 'Y' specifying the name of their respective electrode at which each gas is obtained. One of these gases when reacts with dry calcium hydroxide produces a compound 'Z' which is widely used in water treatment plants and textile industries. Name Z and write chemical equation for the reaction involved in its formation.

(a) Upper half of a convex lens is covered with a black paper. Draw a ray diagram to show the formation of image of an object placed at a distance of 2F from such a lens. Mention the position and nature of the image formed. State the observable difference in the image obtained if the lens is uncovered. Give reason to justify your answer. (b) An object is placed at a distance of 30 cm from the optical centre of a concave lens of focal length 15 cm. Use lens formula to determine the distance of the image from the optical centre of the lens.

(a) (i) Distinguish between hormonal co-ordination in plants and animals. (ii) Which part of the brain is responsible for - (1) intelligence (2) riding a bicycle (3) vomiting (4) controlling hunger (iii) How is brain and spinal-cord protected against mechanical injuries ? OR (b) (i) What are tropic movements ? Give an example of a plant hormone which (1) inhibits growth and (2) promotes cell division. (ii) Explain directional movement of a tendril in pea plant in response to touch. Name the hormone responsible for this movement.

(a) (i) Give reason why carbon can neither form $\mathrm{C}^{4 + }$ cations nor $\mathrm{C}^{4 - }$ anions but form covalent compounds. (ii) What is homologous series of carbon compound ? Write the molecular formula of any two consecutive members of homologous series of aldehydes. (iii) Draw the structure of the molecule of cyclohexane $(\mathrm{C}_6\mathrm{H}_{12})$. OR (b) (i) Name a commercially important carbon compound having functional group -OH and write its molecular formula. (ii) Write chemical equation to show its reaction with (1) Sodium metal (2) Excess conc. sulphuric acid (3) Ethanoic acid in the presence of an acid catalyst (4) Acidified potassium dichromate Also write the name of the product formed in each case.

(A) (i) Define electric power. Express it in terms of potential difference (V) and resistance (R). (ii) An electric oven is designed to work on the mains voltage of 220 V. This oven consumes 11 units of electrical energy in 5 hours. Calculate: (a) power rating of the oven (b) current drawn by the oven (c) resistance of the oven when it is red hot OR (B) (i) Write the relation between resistance R and electrical resistivity $\rho$ of the material of a conductor in the shape of cylinder of length $l$ and area of cross-section A. Hence derive the SI unit of electrical resistivity. (ii) The resistance of a metal wire of length $3\mathrm{m}$ is $60\Omega$ . If the area of cross-section of the wire is $4\times 10^{-7}\mathrm{m}^2$ , calculate the electrical resistivity of the wire. (iii) State how would electrical resistivity be affected if the wire (of part 'ii') is stretched so that its length is doubled. Justify your answer.

(A) (i) Define a homologous series of carbon compounds. (ii) Why is the melting and boiling points of $\mathrm{C_4H_8}$ higher than that of $\mathrm{C_3H_6}$ or $\mathrm{C_2H_4}$ ? (iii) Why do we NOT see any gradation in chemical properties of a homologous series compounds ? (iv) Write the name and structures of (i) aldehyde and (ii) ketone with molecular form $\mathrm{C_3H_6O}$ . OR (B) (i) Write the name and structure of an organic compound 'X' having two carbon atoms in its molecule and its name is suffixed with '-ol'. (ii) What happens when 'X' is heated with excess concentrated sulphuric acid at 443 K? Write chemical equation for the reaction stating the conditions for the reaction. Also state the role played by concentrated sulphuric acid in the reaction. (iii) Name and draw the electron dot structure of hydrocarbon produced in the above reaction.

(A) (i) Name three techniques/devices used by human females to avoid pregnancy. Mention the side effects caused by each. (ii) What will happen if in a human female (a) fertilisation takes place, (b) an egg is not fertilised ? OR (B) (i) Draw a diagram showing spore formation in Rhizopus and label the (a) reproductive and (b) non-reproductive parts. Why does Rhizopus not multiply on a dry slice of bread ? (ii) Name and explain the process by which reproduction takes place in Hydra.

Give reason for the following : (a) During reproduction inheritance of different proteins will lead to altered body designs. (b) Fertilization cannot take place in flowers if pollination does not occur. (c) All multicellular organisms cannot give rise to new individuals through fragmentation or regeneration. (d) Vegetative propagation is practised for growing only some type of plants. (e) The parents and off-springs of organisms reproducing sexually have the same number of chromosomes.

(a) (i) What is meant by resistance of a conductor? Define its SI unit. (ii) List two factors on which the resistance of a rectangular conductor depends. (iii) How will the resistance of a wire be affected if its (1) length is doubled, and (2) radius is also doubled? Give justification for your answer. OR (b) In an electric circuit three bulbs of 100 W each are connected in series to a source. In another circuit set of three bulbs of the same wattage are connected in parallel to the same source. (i) Will the bulb in the two circuits glow with the same brightness? Justify your answer. (ii) Now, let one bulb in both the circuits get fused. Will the rest of the bulbs continue to glow in each circuit? Give reason for your answer.

(a) (i) A compound 'A' with a molecular formula of $C_2H_4O_2$ reacts with a base to give salt and water. Identify 'A', state its nature and the name of the functional group it possesses. Write chemical equation for the reaction involved. (ii) When the above stated compound 'A' reacts with another compound 'B' having molecular formula $C_2H_6O$ in the presence of an acid, a sweet smelling compound 'C' is formed. (1) Identify 'B' and 'C'. (2) State the role of acid in this reaction. (3) Write chemical equation for the reaction involved. OR (b) (i) Name the compound formed when ethanol is heated at $443 \text{ K}$ in the presence of conc. $H_2SO_4$ and draw its electron dot structure. State the role of conc. $H_2SO_4$ in this reaction. (ii) What is hydrogenation ? Explain it with the help of a chemical equation. State the role of this reaction in industry.

(a) (i) Where are testes located in the human males and why? State two function of the testes. (ii) In the human female, one of the ovaries releases an egg every month. State the changes that take place if (1) the egg is fertilized, and (2) the egg is not fertilized. (iii) What is done during the surgical method in males and females to prevent pregnancy? OR (b) (i) What happens when : (1) Leaves of Bryophyllum fall on the soil ? (2) Planaria is cut into many pieces ? (3) Sporangia of Rhizopus on maturation liberate spores ? Mention the modes of reproduction in each of the above three cases. (ii) Write the changes that occur in a flower once the fertilisation has taken place.

(a) State Ohm's Law. (b) Name and define the physical quantity determined by the slope of $V - I$ curve given in the diagram. Use this graph to find the value of this physical quantity in SI units. (c) Establish the relationship between 1 kWh and 1 joule.

(a) A neutral organic compound $X'$ (Molecular formula $\mathrm{C_2H_6O}$) on reacting with acidified $\mathrm{K_2Cr_2O_7}$ gives an organic compound $Y'$ which is acidic in nature. $X'$ reacts with $Y'$ on warming in the presence of conc. $\mathrm{H_2SO_4}$ to give a sweet smelling compound $Z'$. (i) Identify $X'$, $Y'$ and $Z'$. (ii) Write the chemical equations for the reactions in the conversion of (1) $X'$ to $Y'$ and (2) $X'$ to $Z'$. (iii) State the role of (1) acidified $\mathrm{K_2Cr_2O_7}$ in the conversion of $X'$ to $Y'$ and (2) conc. $\mathrm{H_2SO_4}$ in the reaction of $X'$ and $Y'$. (iv) Name the reaction which occurs when $Z'$ reacts with an alkali. OR (b) Carry out the following conversions, stating the condition(s) for each : (i) Ethanol Ethene (ii) Ethene Ethane (iii) Ethane Chloroethane (iv) Ethanol Ethanoic acid (v) Ethanoic acid Ethyl ethanoate

(i) How is electric current related to the potential difference across the terminals of a conductor ? Draw a labelled circuit diagram to verify this relationship. (ii) Why should an ammeter have low resistance ? (iii) Two V - I graphs A and B for series and parallel combinations of two resistors are as shown. Giving reason state which graph shows (a) series, (b) parallel combination of the resistors.

(i) Name and explain the two modes of asexual reproduction observed in hydra. (ii) What is vegetative propagation ? List two advantages of using this technique.

(A) (i) Draw the structure of the following compounds : (a) Butanoic acid (b) Chloropentane (ii) How are structure (i) and structure (ii) given below related to one another ? Give reason to justify your answer. Draw one more possible structure for above case. (iii) Differentiate between saturated and unsaturated carbon compounds on the basis of their general formula. OR (B) (i) What happens when a small piece of sodium is dropped in ethanol ? Write the equation for this reaction. (ii) Why is glacial acetic acid called so ? (iii) What happens when ethanol is heated at $443 K$ in the presence of conc. $H_2SO_4$ ? Write the role of conc. $H_2SO_4$ in this case. (iv) Write an equation showing saponification.

(a) An acid 'X' and an alcohol 'Y' react with each other in the presence of an acid catalyst to form a sweet smelling substance 'Z'. Identify 'X', 'Y' and 'Z'. Write the chemical equation for the reaction involved and name it. The substance 'Z' on treatment with sodium hydroxide produces back the alcohol 'Y' and sodium ethanoate. Write the chemical equation for the reaction involved and name it, giving justification for the name. OR (b) (i) Name the simplest saturated hydrocarbon. Draw its electron dot structure. Which type of bonds exist in this compound? (ii) Name any two mixtures of the carbon compound used as a fuel in daily life, of which the above mentioned compound is an important component. (iii) In which homologous series of carbon compounds can this compound be placed? Write the general formula of the series. (iv) Which type of flame is produced on burning it?

(a) An object is placed in front of a convex lens of focal length f. If the distance of the object from the lens is 2f, draw a ray diagram to show the formation of the image. Write the value of magnification in this case. (b) A student has focussed the image of a candle flame on a white screen using a convex lens. The situation is as given below: Length of the flame $= 2\text{ cm}$ Focal length of the lens $= 12\text{ cm}$ Distance of the flame from the lens $= 16\text{ cm}$ If the flame is perpendicular to the principal axis of the lens, calculate the values of the following: (i) Distance of the image from the lens (ii) Length of the image formed

(a) (i) List three points of difference between nervous and hormonal mechanisms for control and coordination in animals. (ii) How are auxins related with the bending of plant shoot towards unidirectional light? Explain. OR (b) (i) Name the disorder which a person is likely to suffer from due to the following: (I) Over-secretion of growth hormone (II) Deficiency of oestrogen in females (III) Less secretion of thyroxine Also name the gland that secretes each of the hormones mentioned above. (ii) How is the timing and amount of hormone released regulated? Explain with the help of an example.

(a) An electric iron consumes energy at a rate of 880 W when heating is at the maximum rate and 330 W when the heating is at the minimum. If the source voltage is 220 V, calculate the current and resistance in each case. (b) What is heating effect of electric current? (c) Find an expression for the amount of heat produced when a current passes through a resistor for some time.

(a) Name the parts of a bisexual flower that are not directly involved in reproduction. (b) Differentiate between self pollination and cross pollination. List any two significance of pollination. (c) What is the fate of ovules and ovary after fertilization in a flower?

(a) A saturated organic compound 'A' belongs to the homologous series of alcohols. On heating 'A' with concentrated sulphuric acid at 443 K, it forms an unsaturated compound 'B' with molecular mass 28 u. The compound 'B' on addition of one mole of hydrogen in the presence of Nickel, changes to a saturated hydrocarbon 'C'. (i) Identify A, B and C. (ii) Write the chemical equations showing the conversion of A into B. (iii) What happens when compound C undergoes combustion? (iv) State one industrial application of hydrogenation reaction. (v) Name the products formed when compound A reacts with sodium. OR (b) (i) With the help of diagram, show the formation of micelles, when soap is applied on oily dirt. (ii) Take two test tubes X and Y with $10\mathrm{mL}$ of hard water in each. In test tube 'X', add few drops of soap solution and in test tube 'Y' add a few drops of detergent solution. Shake both the test tubes for the same period. (1) In which test tube the formation of foam will be more? Why? (2) In which test tube is a curdy solid formed? Why?

Give reasons: (a) Ventricles have thicker muscular walls than atria. (b) Transport system in plants is slow. (c) Circulation of blood in aquatic vertebrates differs from that in terrestrial vertebrates. (d) During the daytime, water and minerals travel faster through xylem as compared to the night. (e) Veins have valves whereas arteries do not.

(a) Define isomerism. Draw all possible isomers of butane. (b) "A compound 'X' on combustion gives a yellow flame with lots of smoke." What inference would you draw from this statement? (c) State the role of alkaline $KMnO_4$ in the reaction involving conversion of an alcohol to corresponding carboxylic acid.

Two ores X and Y were taken. On heating these ores it was observed that (a) ore X gives $CO_2$ gas, and (b) ore Y gives $SO_2$ gas. Write steps to convert these ores into metals, giving chemical equations of the reactions that take place.

OR (a) With the help of a diagram explain the method of refining of copper by electrolysis. (b) How are broken railway tracks joined? Give the name of the process and the chemical equation of the reaction involved.

OR (a) A person suffering from myopia (near-sightedness) was advised to wear corrective lens of power $-2.5 \text{ D}$. A spherical lens of same focal length was taken in the laboratory. At what distance should a student place an object from this lens so that it forms an image at a distance of $10 \text{ cm}$ from the lens? (b) Draw a ray diagram to show the position and nature of the image formed in the above case.

(a) Draw a labelled ray diagram to show the path of a ray of light incident obliquely on one face of a glass slab. (b) Calculate the refractive index of the material of a glass slab. Given that the speed of light through the glass slab is $2 \times 10^8 \text{ m/s}$ and in air is $3 \times 10^8 \text{ m/s}$. (c) Calculate the focal length of a lens, if its power is $-2.5 \text{ D}$.

(a) Two lamps rated $100 \text{ W}$, $220 \text{ V}$ and $10 \text{ W}$, $220 \text{ V}$ are connected in parallel to $220 \text{ V}$ supply. Calculate the total current through the circuit. (b) Two resistors X and Y of resistances $2 \Omega$ and $3 \Omega$ respectively are first joined in parallel and then in series. In each case the voltage supplied is $5 \text{ V}$. (i) Draw circuit diagrams to show the combination of resistors in each case. (ii) Calculate the voltage across the $3 \Omega$ resistor in the series combination of resistors.

OR (a) Name the mode of reproduction of the following organisms and state the important feature of each mode : (i) Planaria (ii) Hydra (iii) Rhizopus (b) We can develop new plants from the leaves of Bryophyllum. Comment. (c) List two advantages of vegetative propagation over other modes of reproduction.

Based on the given diagram answer the questions given below : (a) Label the parts A, B, C and D. (b) Name the hormone secreted by testis and mention its role. (c) State the functions of B and C in the process of reproduction.

(a) Why is nutrition necessary for the human body? (b) What causes movement of food inside the alimentary canal? (c) Why is small intestine in herbivores longer than in carnivores? (d) What will happen if mucus is not secreted by the gastric glands?

(a) State Fleming's Left-hand rule. (b) List three characteristic features of the electric current used in our homes. (c) What is a fuse? Why is it called a safety device? (d) Why is it necessary to earth metallic electric appliances?

Draw a schematic diagram of a circuit consisting of a battery of 3 cells of $2\text{ V}$ each, a combination of three resistors of $10\Omega$, $20\Omega$ and $30\Omega$ connected in parallel, a plug key and an ammeter, all connected in series. Use this circuit to find the value of the following: (a) Current through each resistor (b) Total current in the circuit (c) Total effective resistance of the circuit OR Two identical resistors, each of resistance $15\Omega$, are connected in (i) series, and (ii) parallel, in turn to a battery of $6\text{ V}$. Calculate the ratio of the power consumed in the combination of resistors in each case.

Draw a neat diagram showing fertilisation in a flower and label (a) Pollen tube, (b) Male germ cell and (c) Female germ cell, on it. Explain the process of fertilisation in a flower. What happens to the (i) ovary and (ii) ovule after fertilisation? OR (a) What is puberty? (b) Describe in brief the functions of the following parts in the human male reproductive system: (i) Testes (ii) Seminal vesicle (iii) Vas deferens (iv) Urethra (c) Why are testes located outside the abdominal cavity? (d) State how sperms move towards the female germ cell.

A cloth strip dipped in onion juice is used for testing a liquid 'X'. The liquid 'X' changes its odour. Which type of an indicator is onion juice? The liquid 'X' turns blue litmus red. List the observations the liquid 'X' will show on reacting with the following: (a) Zinc granules (b) Solid sodium carbonate Write the chemical equations for the reactions involved. OR Define water of crystallisation. Give the chemical formula for two compounds as examples. How can it be proved that the water of crystallisation makes a difference in the state and colour of the compounds?

(a) (i) Write two properties of gold which make it the most suitable metal for ornaments. (ii) Name two metals which are the best conductors of heat. (iii) Name two metals which melt when you keep them on your palm. (b) Explain the formation of ionic compound CaO with electron-dot structure. Atomic numbers of calcium and oxygen are 20 and 8 respectively.

(a) Draw a diagram showing germination of pollen on stigma of a flower and mark on it the following organs/parts: (i) Pollen Grain (ii) Pollen tube (iii) Stigma (iv) Female germ cell (b) State the significance of pollen tube. (c) Name the parts of flower that develop after fertilization into: (i) Seed (ii) Fruit OR (a) "Use of a condom is beneficial for both the sexes involved in a sexual act." Justify this statement giving two reasons. (b) How do oral contraceptive help in avoiding pregnancies? (c) What is sex selective abortion? How does it affect a healthy society? (State any one consequence)

Write balanced chemical equations to explain what happens, when: (i) Mercuric oxide is heated. (ii) Mixture of cuprous oxide and cuprous sulphide is heated. (iii) Aluminium is reacted with manganese dioxide. (iv) Ferric oxide is reduced with aluminium. (v) Zinc carbonate undergoes calcination. OR (i) By the transfer of electrons, illustrate the formation of bond in magnesium chloride and identify the ions present in this compound. (ii) Ionic compounds are solids. Give reasons. (iii) With the help of a labelled diagram show the experimental set up of action of steam on a metal.

(a) Compare soaps and detergents on the basis of their composition and cleansing action in hard water. (b) What happens when ethanol is treated with sodium metal? State the behaviour of ethanol in this reaction. (c) Draw the structure of cyclohexane. (d) Name the following compound: $$\text{CH}_3-\text{CH}_2-\text{OH}$$

(a) Write the correct sequence of steps followed during journey of oxygen rich blood from lungs to various organs of human body. (b) What happens when the system of blood vessels develop a leak?

(a) A security mirror used in a big showroom has radius of curvature 5 m. If a customer is standing at a distance of 20 m from the cash counter, find the position, nature and size of the image formed in the security mirror. (b) Neha visited a dentist in his clinic. She observed that the dentist was holding an instrument fitted with a mirror. State the nature of this mirror and reason for its use in the instrument used by dentist. OR Rishi went to a palmist to show his palm. The palmist used a special lens for this purpose. (i) State the nature of the lens and reason for its use. (ii) Where should the palmist place/hold the lens so as to have a real and magnified image of an object? (iii) If the focal length of this lens is 10 cm and the lens is held at a distance of 5 cm from the palm, use lens formula to find the position and size of the image.

(a) For the combination of resistors shown in the following figure, find the equivalent resistance between M & N. (b) State Joule's law of heating. (c) Why we need a 5 A fuse for an electric iron which consumes 1 kW power at 220 V? (d) Why is it impracticable to connect an electric bulb and an electric heater in series?

OR: (a) Define the following terms: (i) Power of a lens (ii) Principal focus of a concave mirror (b) Write the relationship among the object distance (u), image distance (v) and the focal length (f) of a (i) Spherical lens (ii) Spherical mirror (c) An object is placed at a distance of 10 cm from optical centre of a convex lens of focal length 15 cm. Draw a labelled ray diagram to show the formation of image in this case.

(a) A concave mirror of focal length 10 cm can produce a magnified real as well as virtual image of an object placed in front of it. Draw ray diagrams to justify this statement. (b) An object is placed perpendicular to the principal axis of a convex mirror of focal length 10 cm. The distance of the object from the pole of the mirror is 10 cm. Find the position of the image formed.

(a) List three different categories of contraception methods. (b) Why has Government of India prohibited prenatal sex determination by law? State its benefits in the long run. (c) Unsafe sexual act can lead to various infections. Name two bacterial and two viral infections caused due to unsafe sex.

(a) Find the ratio of resistances of two copper rods X and Y of lengths 30 cm and 10 cm respectively and having radii 2 cm and 1 cm respectively. (b) A current of 500 mA flows in a series circuit containing an electric lamp and a conductor of 10Ω when connected to 6V battery. Find the resistance of the electric lamp.

OR: (a) In the female reproductive system of human beings, state the functions of (i) ovary (ii) oviduct (b) Mention the changes which the uterus undergoes, when (i) it has to receive a zygote. (ii) no fertilization takes place. (c) State the function of placenta.

(a) Describe the structure and function of the basic filtering unit of kidney. (b) List two factors on which reabsorption of water from urine depends?

(a) What is a homologous series? Explain with an example. (b) Define the following terms giving one example of each. (i) Esterification (ii) Addition reaction

OR: What happens when (Write the balanced equation involved) - (i) Copper is heated in air? (ii) Aluminium oxide is reacted with hydrochloric acid? (iii) Potassium reacts with water? (iv) Cinnabar is heated in air? (v) Aluminium oxide reacts with sodium hydroxide?

(a) How is the method of extraction of metals high up in the reactivity series different from that for metals in the middle? Why cannot the same process be applied for them? Name and explain the process of extraction of sodium. (b) Draw a labelled diagram of electrolytic refining of copper.

(a) What is an electromagnet? List any two uses. (b) Draw a labelled diagram to show how an electromagnet is made. (c) State the purpose of soft iron core used in making an electromagnet. (d) List two ways of increasing the strength of an electromagnet if the material of the electromagnet is fixed.

OR An object $4.0\text{ cm}$ in size, is placed $25.0\text{ cm}$ in front of a concave mirror of focal length $15.0\text{ cm}$. (i) At what distance from the mirror should a screen be placed in order to obtain a sharp image? (ii) Find the size of the image. (iii) Draw a ray diagram to show the formation of image in this case.

Draw a ray diagram in each of the following cases to show the formation of image, when the object is placed: (i) between optical centre and principal focus of a convex lens. (ii) anywhere in front of a concave lens. (iii) at 2F of a convex lens. State the signs and values of magnifications in the above mentioned cases (i) and (ii).

(a) What is the law of dominance of traits? Explain with an example. (b) Why are the traits acquired during the life time of an individual not inherited? Explain.

OR (a) Name the organs that form the excretory system in human beings. (b) Describe in brief how urine is produced in human body.

(a) Why is there a difference in the rate of breathing between aquatic organisms and terrestrial organisms? Explain. (b) Draw a diagram of human respiratory system and label - pharynx, trachea, lungs, diaphragm and alveolar sac on it.

OR Define atomic size. Give its unit of measurement. In the modern periodic table what trend is observed in the atomic radius in a group and a period and why is it so?

The position of certain elements in the Modern Periodic Table are shown below. | Group | 1 | 2 | 3 to 12 | 13 | 14 | 15 | 16 | 17 | 18 | | :--- | :---: | :---: | :---: | :---: | :---: | :---: | :---: | :---: | :---: | | **Period 1** | G | | | | | | | | H | | **Period 2** | A | | | I | | | B | | C | | **Period 3** | | D | | | E | | | | F | Using the above table answer the following questions giving reasons in each case: (i) Which element will form only covalent compounds? (ii) Which element is a non-metal with valency 2? (iii) Which element is a metal with valency 2? (iv) Out of H, C and F which has largest atomic size? (v) To which family does H, C and F belong?

Carbon cannot reduce the oxides of sodium, magnesium and aluminium to their respective metals. Why? Where are these metals placed in the reactivity series? How are these metals obtained from their ores? Take an example to explain the process of extraction along with chemical equations.

(a) With the help of a suitable circuit diagram prove that the reciprocal of the equivalent resistance of a group of resistances joined in parallel is equal to the sum of the reciprocals of the individual resistances. (b) In an electric circuit two resistors of $12 \Omega$ each are joined in parallel to a $6 V$ battery. Find the current drawn from the battery.

An electric lamp of resistance $20 \Omega$ and a conductor of resistance $4 \Omega$ are connected to a $6 V$ battery as shown in the circuit. Calculate: (a) the total resistance of the circuit. (b) the current through the circuit. (c) the potential difference across the (i) electric lamp and (ii) conductor, and (d) power of the lamp.

An object is placed at a distance of $60 cm$ from a concave lens of focal length $30 cm$. (i) Use lens formula to find the distance of the image from the lens. (ii) List four characteristics of the image (nature, position, size, erect/inverted) formed by the lens in this case. (iii) Draw ray diagram to justify your answer of part (ii).

Define pollination. Explain the different types of pollination. List two agents of pollination. How does suitable pollination lead to fertilisation?

Write the chemical formula and name of the compound which is the active ingredient of all alcoholic drinks. List its two uses. Write chemical equation and name of the product formed when this compound reacts with: (i) sodium metal (ii) hot concentrated sulphuric acid.

(a) List in tabular form three chemical properties on the basis of which we can differentiate between a metal and a non-metal. (b) Give reasons for the following: (i) Most metals conduct electricity well. (ii) The reaction of iron (III) oxide $[Fe_2O_3]$ with heated aluminium is used to join cracked machine parts.