CBSE Class 10 Science — Chemical Reactions and Equations

(A) Observe the given figure and identify the labelled parts P, Q, R and S. OR (B) Which of the plant hormones are responsible for the following processes? (i) Promote cell division (ii) Inhibition of growth (iii) Detection of light (iv) Wilting of leaves

(i) $\mathrm{AgNO_3 + NaCl \longrightarrow NaNO_3 + AgCl}$ (ii) $\mathrm{K_2SO_4 + BaCl_2 \longrightarrow BaSO_4 + 2KCl}$ Which of the following options clearly describes both the reactions?

The gases evolved on heating lead (II) nitrate crystals are:

Magnesium ribbon burns with a dazzling white flame and changes into a white powder as shown in the diagram. The powder is dissolved in water. Identify the chemical formula of the white powder and the correct change observed when the solution is tested with litmus paper.

The volume ratio of hydrogen and oxygen gases liberated during electrolysis of water is:

Study the following table and select the correct option:

Galvanization is a process of coating iron articles with a thin layer of zinc to prevent iron from rusting. The iron is protected even if the zinc coating is scratched and iron is exposed. Which of the following is/are true about how zinc prevents the rusting of iron? (P) A galvanised iron article does not undergo oxidation. (Q) The zinc coating prevents contact of iron with air. (R) Zinc provides continuous protection to iron from rusting.

Assertion (A): Reaction of quick lime with water is an exothermic reaction. Reason (R): A large amount of heat is evolved on the reaction of quick lime and water.

What happens when (i) potassium iodide solution is added to lead (II) nitrate solution? (ii) zinc is added to copper (II) chloride solution? (iii) hydrogen gas is passed over hot copper (II) oxide? Write balanced chemical equations of the reactions involved in support of your answer.

(a) Name the substance oxidised and reduced in the following reaction: $\mathrm{ZnO + C\longrightarrow Zn + CO}$ (b) Balance the following chemical reaction: $\mathrm{Pb(NO_3)_2 + KI\longrightarrow PbI_2 + KNO_3}$ (c) Give one example each of electrolytic decomposition and decomposition by sunlight.

What happens when (i) Calcium carbonate is heated? (ii) Silver bromide is exposed to sunlight? (iii) Lead is added to copper (II) chloride solution? Write balanced chemical equations of the reactions involved in support of your answer.

The main observations while performing the experiment of burning magnesium ribbon in air are : (i) Magnesium ribbon burns with a dazzling white flame. (ii) A white powder is formed. (iii) Magnesium ribbon vapouriess. (iv) Aqueous solution of the white powder turns blue litmus to red.

In the following experimental setup of electrolysis of water, if P and Q are the gases collected in the test tubes enclosing the electrodes R and S, then select the option/options in which the matching is correct: (i) P-Oxygen gas R-Anode (ii) P-Hydrogen gas R-Cathode (iii) Q-Hydrogen gas S-Cathode (iv) Q-Oxygen gas S-Anode

In which one of the following situations a chemical reaction does not occur?

Consider the following chemical equation : $pAl + qH_2O\longrightarrow rAl_2O_3 + sH_2$ To balance this chemical equation, the values of 'p', 'q', 'r' and 's' must be respectively :

The correct balanced chemical equation showing exothermic reaction in which natural gas burns in air is:

Electrolysis of water is a decomposition reaction. The mass ratio $(M_H : M_O)$ of hydrogen and oxygen gases liberated at the electrodes during electrolysis of water is :

The following table shows the pH values of four solutions A, B, C and D on a pH scale. The solutions A, B, C and D respectively are of a

The values of a, b, c and d in the following balanced chemical equation are respectively: $a Pb(NO_3)_2 \xrightarrow{heat} b PbO + c NO_2 + d O_2$

Which among the following is not a neural action controlled by the part of human brain labelled 'X' in the figure above?

Identify from the following the ray diagram which shows the correct path of the reflected ray for the ray incident on a concave mirror as shown:

Assertion (A) : Decomposition reactions are generally endothermic reactions. Reason (R) : Decomposition of organic matter into compost is an exothermic process.

A light green coloured solution of sulphate salt of metal 'P' is taken in a beaker, a rod of another metal 'Q' is put in this solution as shown the following figures: Identify the metals 'P' and 'Q' and write its chemical equation for the reaction that occurs. State the conclusion of this reaction in terms of reactivity series of metals.

Define oxidation. Identify and name the substance oxidised in the following reaction: $CuO + H_2 → Cu + H_2O$

(a) List the possible sources of energy required in decomposition reactions. Illustrate any one with a suitable example. OR (b) What is observed when hydrated ferrous sulphate crystals are heated in a dry boiling tube? Give balanced chemical equation(s) of the reactions(s) that occur(s).

A student performs the following experiment in his school laboratory. List two observations to justify that in this experiment a chemical change has taken place.

(A) How is lymph formed ? State its important function. OR (B) (a) Identify 'X' in the figure of human nephron shown below. What role does it play in the process of urine formation ? (b) Why some substances are selectively reabsorbed from the initial filtrate of urine, as it flows along the tabular part of nephron ?

Study the figure in which the path of a ray of light going from Medium 1 to Medium 2 is shown. (a) Out of the two Media - Medium 1 and Medium 2, in which is the speed of light more? (b) State reason of bending of the refracted ray away from the normal. (c) Express refractive index of Medium 2 with respect to Medium 1 in terms of speed of light in two media.

Write balanced chemical equation for the reactions that occur when (a) steam is passed over red hot iron. (b) natural gas is burnt in air. (c) glucose reacts with oxygen in the cells of our body and provides energy.

(A) Why do we balance a chemical equation? Name and state the law that suggests the balancing of a chemical equation? Balance the following chemical equation: $Zn + H_3PO_4 → Zn_3(PO_4)_2 + H_2$ OR (B) Define a precipitation reaction. Give its example and also express the reaction that occurs in the form of a balanced chemical equation.

(a) (i) Define the term decomposition reaction. Write one chemical equation each for decomposition reaction where energy is supplied in the form of heat, light or electricity. (ii) Decomposition of vegetable matter into compost is considered an exothermic reaction. Why? OR (b) Why are decomposition reactions called the opposite of combination reactions? Write one chemical equation each for these two types of reactions mentioning the name of the reactant(s) and the product(s) involved in the reactions.

(A) Observe the following diagram showing an experiment to determine the conditions under which a metal 'M' corrodes. List your observations in each of the three cases A, B and C with reason, if the metal 'M' is generally protected against corrosion by the method of galvanisation. OR (B) (a) Show the formation of Aluminium Nitride (AlN) by the transfer of electrons. [At. no. of Al = 13; At. no. of N = 7] (b) "Ionic compounds are solids and are generally brittle and break into pieces when pressure is applied." Give reason to justify the statement.

Consider the following electric circuit : Calculate the values of the following : (a) The total resistance of the circuit (b) The total current drawn from the source (c) Potential difference across the parallel combination of $10\ \Omega$ and $15\ \Omega$ resistors

(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) (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.

Common salt is a very important chemical compound for our daily life. It's chemical name is sodium chloride and it is used as a raw material in the manufacture of caustic soda, washing soda, baking soda etc. It is also used in the preservation of pickles, butter, meat etc. (i) Name the acid and the base from which common salt can be obtained. (ii) State the nature (acidic/basic/neutral) of sodium chloride. Give reason for the justification for your answer. (iii) (A) What happens when electric current is passed through an aqueous solution of sodium chloride (called brine)? Name the products obtained along with the corresponding places in the electrolytic cell where each of these products is obtained. OR (iii) (B) How is washing soda obtained from sodium chloride? Give chemical equation of the reactions involved in the process.

The growth movements of plant parts in which the direction of the stimulus determines the direction of the response is known as tropic movements or tropism. Plants also have non-directional movements which may not be growth dependent. (I) Name the movement which causes 'X' and 'Y' to grow downwards and upwards respectively. (II) Write the name of a hormone that plays a major role in (i) falling of leaves (ii) rapid cell division. (III) (a) Leaves of the sensitive plant move very quickly in response to 'touch'. How is this stimulus of touch communicated and explain how the movement takes place. OR (III) (b) Name the plant hormone which is synthesized at the shoot tip. How does this hormone helps the plant to bend towards light?

Study the circuit shown in which two resistors X and Y of resistances $3 \Omega$ and $6 \Omega$ respectively are joined in series with a battery of $2 \text{ V}$. (I) Draw a circuit diagram showing the above two resistors X and Y joined in parallel with same battery and same ammeter and voltmeter. (II) In which combination of resistors will the (i) potential difference across X and Y and (ii) current through X and Y, be the same? (III) (a) Find the current drawn from the battery by the series combination of the two resistors (X and Y). OR (III) (b) Determine the equivalent resistance of the parallel combination of the two resistors (X and Y).

When 2 mL of sodium hydroxide solution is added to few pieces of granulated zinc in a test tube and then warmed, the reaction that occurs can be written in the form of a balanced chemical equation as :

To balance the following chemical equation, the values of the coefficients $x, y$ and $z$ must be respectively : $x \mathrm{Zn(NO_3)_2 \xrightarrow{\Delta} y \mathrm{ZnO + z \mathrm{NO_2 + O_2}}}$

Identify the product 'X' obtained in the following chemical reaction: $CaCO_3 \xrightarrow{\Delta} X + CO_2$

$\mathrm{Zn + 2CH_3COOH \longrightarrow (CH_3COO)_2Zn + H_2}$ The above reaction is a :

Solid Calcium oxide reacts vigorously with water to form Calcium hydroxide accompanied by the liberation of heat. From the information given above it may be concluded that this reaction

Which of the following is a redox reaction, but not a combination reaction?

Select from the following a decomposition reaction in which source of energy for decomposition is light :

A metal and a non-metal that exists in liquid state at the room temperature are respectively :

Select from the following a process in which a combination reaction is involved :

Consider the following compounds : $\mathrm{FeSO_4}$ ; $\mathrm{CuSO_4}$ ; $\mathrm{CaSO_4}$ ; $\mathrm{Na_2CO_3}$ The compound having maximum number of water of crystallisation in its crystalline form in one molecule is :

Consider the following Chemical equation: $aAl_2O_3 + bHCl \longrightarrow cAlCl_3 + dH_2O$. In order to balance this chemical equation, the values of a, b, c and d must be

Identify the correct statement about the following reaction : $2\mathrm{H}_2\mathrm{S} + \mathrm{SO}_2 \longrightarrow 2\mathrm{H}_2\mathrm{O} + \mathrm{S}$

$\mathrm{MnO_2 + 4HCl \rightarrow MnCl_2 + 2H_2O + Cl_2}$ The reaction given above is a redox reaction because in this case :

Which one of the following reactions is different from the remaining three?

In a nerve cell, the site where the electrical impulse is converted into a chemical signal is known as :

A stomata closes when : (i) it needs carbon dioxide for photosynthesis. (ii) it does not need carbon dioxide for photosynthesis. (iii) water flows out of the guard cells. (iv) water flows into the guard cells. The correct reason(s) in this process is/are :

At what distance from a convex lens should an object be placed to get an image of the same size as that of the object on a screen ?

The lens system of human eye forms an image on a light sensitive screen, which is called as :

Consider the following combinations of resistors: The combinations having equivalent resistance $1 \Omega$ is/are :

Study the I-V graph for three resistors of resistances $\mathrm{R}_1$, $\mathrm{R}_2$ and $\mathrm{R}_3$ and select the correct statement from the following:

A uniform magnetic field exists in the plane of paper as shown in the diagram. In this field, an electron (e⁻) and a positron (p⁺) enter as shown. The electron and positron experience forces :

Identify the food chain in which the organisms of the second trophic level are missing :

In which of the following organisms, multiple fission is a means of asexual reproduction ?

Assertion (A) : Hydrogen gas is not evolved when zinc reacts with nitric acid. Reason (R) : Nitric acid oxidises the hydrogen gas produced to water and itself gets reduced.

Assertion (A) : Accumulation of harmful chemicals is maximum in the organisms at the highest trophic level of a food chain. Reason (R) : Harmful chemicals are sprayed on the crops to protect them from diseases and pests.

Assertion (A): The rate of breathing in aquatic organisms is much faster than in terrestrial organisms. Reason (R): The amount of oxygen dissolved in water is very high as compared to the amount of oxygen in air.

Assertion (A): The rainbow is a natural spectrum of sunlight in the sky. Reason (R): Rainbow is formed in the sky when the sun is overhead and water droplets are also present in air.

When magnesium ribbon is burnt in air, an ash of white colour is produced. Write chemical equation for the reaction giving the chemical name of the ash produced. State the type of chemical reaction giving justification for your answer.

(a) Copper powder is taken in a china dish and heated over a burner. Name the product formed and state its colour. Write the chemical equation for the reaction involved. OR (b) Write chemical equation for the chemical reaction which occurs when the aqueous solutions of barium chloride and sodium sulphate react together. Write the symbols of the ions present in the compound precipitated in the reaction.

(a) "No precipitation reaction can occur without exchange of ions between the two reactants." Justify this statement giving a balanced chemical equation for the reaction. OR (b) Giving one example of each, differentiate between a displacement reaction and a double displacement reaction.

Name the type of chemical reaction in which calcium oxide reacts with water. Justify your answer by giving balanced chemical equation for the chemical reaction.

State one role of each of the following in human digestive system: (i) Hydrochloric acid (ii) Villi (iii) Anal Sphincter (iv) Lipase

(A) How is the movement of leaves of a sensitive plant different from the downward movement of the roots? OR (B) There is a hormone which regulates carbohydrate, protein and fat metabolism in our body. Name the hormone and the gland which secretes it. Why is it important for us to have iodised salt in our diet?

An object is placed at a distance of $10\mathrm{cm}$ from a convex mirror of focal length $15\mathrm{cm}$. Find the position of the image formed by the mirror.

Use Ohm's law to determine the potential difference across the $3 \Omega$ resistor in the circuit shown in the following diagram when key is closed:

Write one chemical equation each for the chemical reaction in which the following have taken place : (i) Change in colour (ii) Change in temperature (iii) Formation of precipitate Mention colour change/temperature change (rise/fall)/compound precipitated along with equation.

Study the experimental set- up shown in the diagram and write chemical equation for the chemical reaction involved. Name and define the type of reaction. List two other metals which can be used in place of iron to show the same type of reaction with copper sulphate solution.

(i) The pH of a sample of tomato juice is 4.6. How is this juice likely to be in taste ? Give reason to justify your answer. (ii) How do we differentiate between a strong acid and a weak base in terms of ion- formation in aqueous solutions ? (iii) The acid rain can make the survival of aquatic animals difficult. How ?

Define reflex action. With the help of a flow chart show the path of a reflex action such as sneezing.

(a) State Ohm's law. Write formula for the equivalent resistance $R_p$ of the parallel combination of three resistors of values $R_1$, $R_2$ and $R_3$. (b) Find the resistance of the following network of resistors:

(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) 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.

The metals produced by various reduction processes are not very pure. They contain impurities, which must be removed to obtain pure metals. The most widely used method for refining impure metals is electrolytic refining. (i) What is the cathode and anode made of in the refining of copper by this process? (ii) Name the solution used in the above process and write its formula. (iii) (A) How copper gets refined when electric current is passed in the electrolytic cell? OR (iii) (B) You have two beakers 'A' and 'B' containing copper sulphate solution. What would you observe after about 2 hours if you dip a strip of zinc in beaker 'A' and a strip of silver in beaker 'B'? Give reason for your observations in each case.

Mendel worked out the rules of heredity by working on garden pea using a number of visible contrasting characters. He conducted several experiments by making a cross with one or two pairs of contrasting characters of pea plant. On the basis of his observations he gave some interpretations which helped to study the mechanism of inheritance. (i) When Mendel crossed pea plants with pure tall and pure short characteristics to produce $\mathrm{F}_1$ progeny, which two observations were made by him in $\mathrm{F}_1$ plants? (ii) Write one difference between dominant and recessive trait. (iii) (A) In a cross with two pairs of contrasting characters RRYY $\times$ rryy (Round Yellow) (Wrinkled Green) Mendel observed 4 types of combinations in $\mathrm{F}_2$ generation. By which method did he obtain $\mathrm{F}_2$ generation? Write the ratio of the parental combinations obtained and what conclusions were drawn from this experiment. OR (iii) (B) Justify the statement: 'It is possible that a trait is inherited but may not be expressed.'

In a domestic circuit five LED bulbs are arranged as shown. The source voltage is 220 V and the power rating of each bulb is marked in the circuit diagram. Based on the following circuit diagram, answer the following questions: (a) State what happens when (i) key $K_1$ is closed. (ii) key $K_2$ is closed. (b) Find the current drawn by the bulb B when it glows. (c) Calculate (i) the resistance of bulb B, and (ii) total resistance of the combination of four bulbs B, C, D and E. OR (c) What would happen to the glow of all the bulbs in the circuit when keys $K_1$ and $K_2$ both are closed and the bulb C suddenly get fused? Give reason to justify your answer.

Study the data given below showing the focal length of three concave mirrors A, B and C and the respective distances of objects placed in front of the mirrors: | Case | Mirror | Focal Length (cm) | Object Distance (cm) | |---|---|---|---| | 1 | A | 20 | 45 | | 2 | B | 15 | 30 | | 3 | C | 30 | 20 | (i) In which one of the above cases the mirror will form a diminished image of the object? Justify your answer. (ii) List two properties of the image formed in case 2. (iii) (A) What is the nature and size of the image formed by mirror C? Draw ray diagram to justify your answer. OR (iii) (B) An object is placed at a distance of $18\mathrm{cm}$ from the pole of a concave mirror of focal length $12\mathrm{cm}$ . Find the position of the image formed in this case.

Which of the following is an example of endothermic process ?

The balanced chemical equation showing reaction between quicklime and water is :

When aqueous solutions of potassium iodide and lead nitrate are mixed, an insoluble substance separates out. The chemical equation for the reaction involved is :

The emission of brown fumes in the given experimental set-up is due to

In the given experimental set-up, if the experiment is carried out separately with each of the following solutions the cases in which the bulb will glow is/are : (i) Dilute hydrochloric acid (ii) Dilute sulphuric acid (iii) Glucose solution (iv) Alcohol

Select the appropriate state symbols of the products given as X and Y in the following chemical equation by choosing the correct option from table given below : $Zn_{(s)} + H_2SO_{4(l)} \longrightarrow ZnSO_{4(X)} + H_2(Y)$ Table: | | (X) | (Y) | |---|---|---| | (a) | (s) | (l) | | (b) | (aq) | (g) | | (c) | (aq) | (s) | | (d) | (g) | (aq) |

Study the following chemical reaction : $2\mathrm{Na(s)} + 2\mathrm{H}_2\mathrm{O(l)}\longrightarrow 2\mathrm{NaOH(aq)} + \mathrm{H}_2(\mathrm{g})\uparrow$. The reducing agent in this reaction is :

In order to balance the following chemical equation, the values of the coefficients x and y respectively are : $x\text{Pb(NO}_3)_2 \xrightarrow{\text{Heat}} 2\text{PbO} + y\text{NO}_2 + \text{O}_2$

A metal ribbon 'X' burns in oxygen with a dazzling white flame forming a white ash 'Y'. The correct description of X, Y and the type of reaction is :

$\mathrm{MnO}_2 + x\mathrm{HCl} \rightarrow \mathrm{MnCl}_2 + y\mathrm{H}_2\mathrm{O} + z\mathrm{Cl}_2$ In order to balance the above chemical equation, the values of $x$, $y$ and $z$ respectively are:

In the given diagram of a closed stomata : (1), (2), (3) and (4) respectively are

In the following diagram, identify the cells through which massive amounts of gaseous exchange takes place for photosynthesis :

Study the given figure of a Food web and identify the primary consumer in the food web:

Choose the correct order of the stages of binary fission in Leishmania.

Consider the following chemical equation I and II I. $Mg + 2HCl \longrightarrow MgCl_2 + H_2$ II. $NaOH + HCl \longrightarrow NaCl + H_2O$ The correct statement about these equations is -

In the following diagram showing dispersion of white light by a glass prism, the colours 'P' and 'Q' respectively are -

Consider the following three flowers namely X, Y and Z. Which flower(s) would develop into a fruit?

In the following diagram, the position of the needle is shown on the scale of a voltmeter. The least count of the voltmeter and the reading shown by it respectively are:

A positron enters a uniform magnetic field at right angles to it as shown. The direction of force experienced by the positron will be :

Assertion (A): The colour of aqueous solution of copper sulphate turns colourless when a piece of lead is added to it. Reason (R): Lead is more reactive than copper, and hence displaces copper from its salt solution.

Assertion (A) : Reaction of Quicklime with water is an exothermic reaction. Reason (R) : Quicklime reacts vigorously with water releasing a large amount of heat.

State whether the given chemical reaction is a redox reaction or not. Justify your answer. $MnO_2 + 4HCl \longrightarrow MnCl_2 + 2H_2O + Cl_2$

(a) What is observed when aqueous solutions of potassium iodide and lead nitrate are mixed together? Name the type of reaction and write the chemical equation for the reaction that occurs. OR (b) When copper powder is heated in a watch glass, a black substance is formed. (i) Why is this black substance formed? Name it. (ii) How can this black substance be reversed to its original form?

(a) Which one of the two media is denser w.r.t. other medium? Justify your answer (based on a ray entering from medium A to B). (b) If the speed of light in medium A is $v_a$ and in medium B is $v_b$, what is the refractive index of B with respect to A. OR (a) A ray of light starting from diamond is incident on the interface separating diamond and water. Draw a labelled ray diagram to show the refraction of light in this case. (b) Absolute refractive indices of diamond and water are 2.42 and 1.33 respectively. Find the value of refractive index of water w.r.t. diamond.

Silver chloride kept in a china dish turns grey in sunlight. (a) Write the colour of silver chloride when it was kept in the china dish. (b) Name the type of chemical reaction taking place and write the chemical equation for the reaction. (c) State one use of the reaction. Name one more chemical which can be used for the same purpose.

(a) Identify the reducing agent in the following reactions: (i) $4\mathrm{NH}_3 + 5\mathrm{O}_2 \rightarrow 4\mathrm{NO} + 6\mathrm{H}_2\mathrm{O}$ (ii) $\mathrm{H}_2\mathrm{O} + \mathrm{F}_2 \rightarrow \mathrm{HF} + \mathrm{HOF}$ (iii) $\mathrm{Fe}_2\mathrm{O}_3 + 3\mathrm{CO} \rightarrow 2\mathrm{Fe} + 3\mathrm{CO}_2$ (iv) $2\mathrm{H}_2 + \mathrm{O}_2 \rightarrow 2\mathrm{H}_2\mathrm{O}$ (b) Define a redox reaction in terms of gain or loss of oxygen.

(a) Define a double displacement reaction. (b) Write the chemical equation of a double displacement reaction which is also a (i) Neutralization reaction and (ii) Precipitation reaction. Give justification for your answer.

(i) While electrolysing water before passing the current some drops of an acid are added. Why ? Name the gases liberated at cathode and anode. Write the relationship between the volume of gas collected at anode and the volume of gas collected at cathode. (ii) What is observed when silver chloride is exposed to sunlight ? Give the type of reaction involved.

With the help of suitable chemical equations, list the two main differences between roasting and calcination. How is metal reduced from the product obtained after roasting/calcination of the ore? Write the chemical equation for the reaction involved.

(a) Name the gland and the hormone secreted by it in scary situations in human beings. List any two responses shown by our body when this hormone is secreted into the blood. OR (b) In the given diagram (i) Name the parts labelled A, B, and C. (ii) Write the functions of A and C. (iii) Reflex arcs have evolved in animals ? Why ?

(a) (i) What is the first step in the breakdown of glucose during aerobic and anaerobic respiration? Where does it take place? (ii) ATP is called the energy currency of the cell. Why? (iii) What is meant by "residual volume of air" in a breathing cycle? OR (b) Write in sequence the steps for experimental verification of the fact that "sunlight is essential for photosynthesis".

With the help of an appropriate example, justify that some of the chemical reactions are determined by (a) Change in temperature, (b) Evolution of a gas, and (c) Change in colour Give chemical equation for the reaction involved in each case.

Name the hormone released and the gland which secretes it in human beings during scary situations. How does the body respond to enable it to deal with the situation?

(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.

Consider the following electrical circuit diagram in which nine identical resistors of $3\Omega$ each are connected as shown. If the reading of the ammeter $A_1$ is 1 ampere, answer the following questions : (a) What is the relationship between the readings of $A_1$ and $A_3$ ? Give reasons for your answer. (b) What is the relationship between the readings of $A_2$ and $A_3$ ? (c) Determine the reading of the voltmeter $V_1$. OR (c) Find the total resistance of the circuit.

(b) Calculate the equivalent resistance of the following electric circuit: [Circuit diagram not provided]

(a) An electric heater rated $1100\text{ W}$ operates at $220\text{ V}$. Calculate (i) its resistance, and (ii) the current drawn by it.

(a) Three resistors $R_1$, $R_2$ and $R_3$ are connected in parallel and the combination is connected to a battery, an ammeter, a voltmeter and a key. Draw suitable circuit diagram to show the arrangement of these circuit components along with the direction of current flowing. (b) Calculate the equivalent resistance of the following network:

Study the following electric circuit in which the resistors are arranged in three arms A, B and C: (a) Find the equivalent resistance of arm A. (1 mark) (b) Calculate the equivalent resistance of the parallel combination of the arms B and C. (1 mark) (c) (i) Determine the current that flows through the ammeter. (2 marks) OR (ii) Determine the current that flows in the ammeter when the arm B is withdrawn from the circuit. (2 marks)

Write the number of valence electrons present in a nitrogen atom $(\frac{14}{7} \text{N})$.

Define the term induced electric current.

Answer question numbers 3(a) - 3(d) on the basis of your understanding of the following paragraph and the related studied concepts: Around the year 1800, only 30 elements were known. Dobereiner in 1817 and Newlands in 1866 tried to arrange the then known elements and framed laws which were rejected by the scientists. Even after the rejection of the proposed laws, many scientists continued to search for a pattern that correlated the properties of elements with their atomic masses. The main credit for classifying elements goes to Mendeleev for his most important contribution to the early development of a Periodic table of elements wherein he arranged the elements on the basis of their fundamental property, the atomic mass and also on the similarity of chemical properties. The formulae of their hydrides and oxides were treated as basic criteria for the classification of the elements. However, Mendeleev's classification also had some limitations as it could not assign the position to isotopes. He also left some gaps in the periodic table. 3(a) State Mendeleev's Periodic Law. 3(b) Why did Mendeleev leave some gaps in the Periodic table? 3(c) If the letter 'R' was used to represent any of the elements in the group, then the hydride and oxide of carbon would respectively be represented as: (i) $\text{RH}_4$, $\text{RO}$ (ii) $\text{RH}_4$, $\text{RO}_2$ (iii) $\text{RH}_2$, $\text{RO}_2$ (iv) $\text{RH}_2$, $\text{RO}$ 3(d) Isotopes are: (i) Atoms of an element with similar chemical properties but different atomic masses. (ii) Atoms of different elements with similar chemical properties but different atomic masses. (iii) Atoms of an element with different chemical properties but same atomic masses. (iv) Atoms of different elements with different chemical properties but same atomic masses.

OR When hydrogen sulphide gas is passed through a blue solution of copper sulphate, a black precipitate of copper sulphide is obtained and the sulphuric acid so formed remains in the solution. The reaction is an example of a:

Calcium oxide reacts vigorously with water to produce slaked lime. $$\mathrm{CaO(s) + H_2O(l) \rightarrow Ca(OH)_2(aq)}$$ This reaction can be classified as: (A) Combination reaction (B) Exothermic reaction (C) Endothermic reaction (D) Oxidation reaction Which of the following is a correct option?

In a double displacement reaction such as the reaction between sodium sulphate solution and barium chloride solution: (A) exchange of atoms takes place (B) exchange of ions takes place (C) a precipitate is produced (D) an insoluble salt is produced The correct option is:

Identify 'x', 'y' and 'z' in the following reaction: $2\mathrm{KClO}_{3}(x)\xrightarrow{(y)}\mathrm{2KCl}(x)+\mathrm{O}_{2}(z)$

Strong heating of ferrous sulphate leads to the formation of a brown solid and two gases. This reaction can be categorised as

In which of the following, the identity of initial substance remains unchanged?

Assertion (A): Following is a balanced chemical equation for the action of steam on iron: $3\text{Fe} + 4\text{H}_2\text{O} \longrightarrow \text{Fe}_3\text{O}_4 + 4\text{H}_2$. Reason (R): The law of conservation of mass holds good for a chemical equation.

Mention with reason the colour changes observed when: (i) silver chloride is exposed to sunlight. (ii) copper powder is strongly heated in the presence of oxygen. (iii) a piece of zinc is dropped in copper sulphate solution.

Lead nitrate solution is added to a test tube containing potassium iodide solution. (a) Write the name and colour of the compound precipitated. (b) Write the balanced chemical equation for the reaction involved. (c) Name the type of this reaction justifying your answer. OR What happens when food materials containing fats and oils are left for a long time? List two observable changes and suggest three ways by which this phenomenon can be prevented.

A compound 'A' is used in the manufacture of cement. When dissolved in water, it evolves a large amount of heat and forms compound 'B'. (i) Identify A and B. (ii) Write chemical equation for the reaction of A with water. (iii) List two types of reaction in which this reaction may be classified.

A shining metal 'M', on burning gives a dazzling white flame and changes to a white powder 'N'. (a) Identify 'M' and 'N'. (b) Represent the above reaction in the form of a balanced chemical equation. (c) Does 'M' undergo oxidation or reduction in this reaction? Justify.

$1\text{ g}$ of copper powder was taken in a China dish and heated. What change takes place on heating? When hydrogen gas is passed over this heated substance, a visible change is seen in it. Give the chemical equations of reactions, the name and the color of the products formed in each case.

OR A chemical compound 'X' is used in the soap and glass industry. It is prepared from brine. (a) Write the chemical name, common name and chemical formula of 'X'. (b) Write the equation involved in its preparation. (c) What happens when it is treated with water containing Ca or Mg salts?

In the electrolysis of water (a) Name the gases liberated at anode and cathode. (b) Why is it that the volume of gas collected on one electrode is two times that on the other electrode? (c) What would happen if dil. $H_2SO_4$ is not added to water?

How it can be proved that the basic structure of the Modern Periodic Table is based on the electronic configuration of atoms of different elements?

The electronic configuration of an element is 2, 8, 4. State its: (a) group and period in the Modern Periodic Table. (b) name and write its one physical property.

2 g of silver chloride is taken in a china dish and the china dish is placed in sunlight for sometime. What will be your observation in this case? Write the chemical reaction involved in the form of a balanced chemical equation. Identify the type of chemical reaction.

Identify the type of reactions taking place in each of the following cases and write the balanced chemical equation for the reactions. (a) Zinc reacts with silver nitrate to produce zinc nitrate and silver. (b) Potassium iodide reacts with lead nitrate to produce potassium nitrate and lead iodide.

Identify the acid and the base from which sodium chloride is obtained. Which type of salt is it? When is it called rock salt? How is rock salt formed?

What is a rainbow? Draw a labelled diagram to show the formation of a rainbow.

Define an ecosystem. Draw a block diagram to show the flow of energy in an ecosystem.

How can we help in reducing the problem of waste disposal? Suggest any three methods.

What is water harvesting? List two main advantages associated with water harvesting at the community level. Write two causes for the failure of sustained availability of groundwater.

(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.

What is methane? Draw its electron dot structure. Name the type of bonds formed in this compound. Why are such compounds: (i) poor conductors of electricity? and (ii) have low melting and boiling points? What happens when this compound burns in oxygen?

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) Identify the given diagram. Name the parts 1 to 5. (b) What is contraception? List three advantages of adopting contraceptive measures.

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

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).

(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.

Draw a labelled diagram in proper sequence to show budding in Hydra.

A student is observing the temporary mount of a leaf peel under a microscope. Draw labelled diagram of the structure of stomata as seen under the microscope.

While studying the dependence of potential difference (V) across a resistor on the current (I) passing through it, in order to determine the resistance of the resistor, a student took 5 readings for different values of current and plotted a graph between V and I. He got a straight line graph passing through the origin. What does the straight line signify? Write the method of determining resistance of the resistor using this graph.

What would you suggest to a student if while performing an experiment he finds that the pointer needle of the ammeter and voltmeter do not coincide with the zero marks on the scales when circuit is open? No extra ammeter/ voltmeter is available in the laboratory.

List four precautions which a student should observe while determining the focal length of a given convex lens by obtaining image of a distant object on a screen.

What is observed when a solution of sodium sulphate is added to a solution of barium chloride taken in a test tube? Write equation for the chemical reaction involved and name the type of reaction in this case.

Write the molecular formula of the 2nd and the 3rd member of the homologous series whose first member is methane.

Write the molecular formula of the $2^{nd}$ and $3^{rd}$ member of the homologous series whose first member is ethene.

In the following food chain, 100 J of energy is available to the lion. How much energy was available to the producer? Plants ⟶ Deer ⟶ Lion

Newly formed DNA copies may not be identical at times. Give one reason.

In the following food chain, plants provide 500 J of energy to rats. How much energy will be available to hawks from snakes ? Plants $\rightarrow$ Rats $\rightarrow$ Snakes $\rightarrow$ Hawks

Write the structural formula of ethanol. What happens when it is heated with excess of conc. $H_2SO_4$ at 443 K? Write the chemical equation for the reaction stating the role of conc. $H_2SO_4$ in this reaction.

While studying the saponification reaction, what do you observe when you mix an equal amount of colourless vegetable oil and 20% aqueous solution of NaOH in a beaker?

A student requires hard water for an experiment in his laboratory which is not available in the neighbouring area. In the laboratory there are some salts, which when dissolved in distilled water can convert it into hard water. Select from the following groups of salts, a group, each salt of which when dissolved in distilled water will make it hard.

To perform an experiment to identify the different parts of an embryo of a dicot seed, first of all you require a dicot seed. Select dicot seeds from the following group: Wheat, Gram, Maize, Pea, Barley, Ground-nut

Describe an activity to show that the colours of white light splitted by a glass prism can be recombined to get white light by another identical glass prism. Also draw ray diagram to show the recombination of the spectrum of white light.

In the following ray diagram the correctly marked angle are:

Show four different ways in which four resistors of $r\ \Omega$ each may be connected in a circuit. In which case is the equivalent resistance of the combination: (i) maximum; (ii) minimum?

(i) Establish a relationship to determine the equivalent resistance $R$ of a combination of three resistors having resistances $R_1$, $R_2$ and $R_3$ connected in parallel. (ii) Three resistors are connected in an electrical circuit. Calculate the resistance between A and B.

The colour of $\text{Cu}$ metal is:

Shashank was asked to carry out a displacement reaction which would show the following: (i) Formation of colourless solution (ii) Black deposits The reactants he should use are:

An iron nail is dipped in the solution of copper sulphate for about 30 minutes, state the change in colour observed. Give the reason for the change.

A student takes 2 mL acetic acid in a dry test tube and adds a pinch of sodium hydrogen carbonate to it. He makes the following observations: I. A colourless and odourless gas evolves with a brisk effervescence. II. The gas turns lime water milky when passed through it. III. The gas burns with an explosion when a burning splinter is brought near it. IV. The gas extinguishes the burning splinter that is brought near it. The correct observations are:

In an experiment to study the properties of acetic acid a student takes about 2 mL of acetic acid in a dry test tube. He adds about 2 mL of water to it and shakes the test tube well. He is likely to observe that:

Read the following statements: I. When a red litmus paper is dipped into reaction mixture of a saponification reaction, it turns blue and the reaction is exothermic. II. When a blue litmus paper is dipped into reaction mixture of a saponification reaction, its colour does not change and the reaction is exothermic. III. When a red litmus paper is dipped into reaction mixture of a saponification reaction, its colour does not change and the reaction is endothermic. IV. When a blue litmus paper is dipped into reaction mixture of a saponification reaction, its colour does not change and the reaction is endothermic. Which of the above statements are correct:

The colours of aqueous solutions of $CuSO_4$ and $FeSO_4$ as observed in the laboratory are :

Some crystals of ferrous sulphate were dissolved in distilled water. The colour of the solution obtained was

Solutions of copper sulphate, iron sulphate and zinc sulphate are prepared and marked I, II and III respectively. Few pieces of aluminium are added to each solution. After some time a change will be observed in

A student prepared an aqueous solution of $CuSO_4$ in beaker X and an aqueous solution of $FeSO_4$ in beaker Y. He then dropped some iron pieces in beaker X and some zinc pieces in beaker Y. After about 10 hours he observed that the solutions in X and Y respectively appear:

Draw the structure for ethanoic acid molecule, $CH_3COOH$.

Give an example of a phenomenon where Tyndall effect can be observed.

What is meant by biological magnification ?

Give an example to illustrate that indiscriminate use of pesticides may result in the degradation of the environment.

How does the valency of elements vary (i) in going down a group, and (ii) in going from left to right in a period of the periodic table ?

In the modern periodic table, the element Calcium (atomic number = 20) is surrounded by elements with atomic numbers 12, 19, 21 and 38. Which of these elements has physical and chemical properties resembling those of Calcium and why ?

State any four characteristics of the image of an object formed by a plane mirror.

Draw a ray diagram to show the refraction of light through a glass prism. Mark on it (a) the incident ray, (b) the emergent ray and (c) the angle of deviation.

Explain with the help of a diagram, how we are able to observe the sunrise about two minutes before the sun gets above the horizon.

List any four reasons for vegetative propagation being practised in the growth of some type of plants.

Describe the role of fallopian tubes in the female reproductive system.

List any four disadvantages of using fossil fuels for the production of energy.

Give two examples each of the following : (i) Renewable sources of energy (ii) Non-renewable sources of energy

Write chemical equations for what happens when (i) sodium metal is added to ethanoic acid. (ii) solid sodium carbonate is added to ethanoic acid. (iii) ethanoic acid reacts with a dilute solution of sodium hydroxide.

The atomic number of an element is 16. Predict (i) the number of valence electrons in its atom (ii) its valency (iii) its group number (iv) whether it is a metal or a non-metal (v) the nature of oxide formed by it (vi) the formula of its chloride

(a) State two properties of carbon which lead to a very large number of carbon compounds. (b) Why does micelle formation take place when soap is added to water ? Why are micelles not formed when soap is added to ethanol ? OR Explain isomerism. State any four characteristics of isomers. Draw the structures of possible isomers of butane, $C_4H_{10}$.

Iron nails were dipped in an aqueous solution of copper sulphate. After about 30 minutes, it was observed that the colour of the solution changed from

A cleaned aluminium foil was placed in an aqueous solution of zinc sulphate. When the aluminium foil was taken out of the zinc sulphate solution after 15 minutes, its surface was found to be coated with a silvery grey deposit. From the above observation it can be concluded that

Vapours of acetic acid smell

Acetic acid reacts with solid sodium hydrogen carbonate

What changes in the colour of iron nails and copper sulphate solution do you observe after keeping the iron nails dipped in copper sulphate solution for about 30 minutes ?

What happens when an aqueous solution of sodium sulphate reacts with an aqueous solution of barium chloride ? State the physical conditions of reactants in which the reaction between them will not take place. Write the balanced chemical equation for the reaction and name the type of reaction.

No chemical reaction takes place when granules of a solid, A, are mixed with the powder of another solid, B. However when the mixture is heated, a reaction takes place between its components. One of the products, C, is a metal and settles down in the molten state while the other product, D, floats over it. It was observed that the reaction is highly exothermic. (i) Based on the given information make an assumption about A and B and write a chemical equation for the chemical reaction indicating the conditions of reaction, physical state of reactants and products and thermal status of reaction. (ii) Mention any two types of reactions under which above chemical reaction can be classified.