CBSE Class 10 Science 2023 Question Paper

Select a pair of olfactory indicators from the following :

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

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 :

Fresh milk has a pH of 6. To delay its curdling, a chemical substance is added to it, which is :

Which of the following statements is true for an amphoteric oxide ?

Hydronium ions are formed by the reaction between :

The correct representation of covalent bonding in an oxygen molecule is :

The process in which loss of water in the form of vapours from the aerial parts of plants takes place is $X$, which helps in $Y$. Here $X$ and $Y$ respectively are:

As compared to terrestrial organisms, the rate of breathing in aquatic organisms is:

Consider the following two statements: (i) The trait that expresses itself in $\mathrm{F}_1$ generation. (ii) The trait that keeps on passing from one generation to another. The appropriate terms for the statements (i) and (ii) respectively are:

The part in which gustatory receptors are present in our body is:

The bacterial and the viral infections that may be caused due to unsafe sex respectively are:

The expressions that relate (i) Q, I and t and (ii) Q, V and W respectively are (Here the symbols have their usual meanings):

A constant current flows in a horizontal wire in the plane of the paper from east to west as shown in the figure. The direction of the magnetic field will be north to south at a point:

An electric kettle consumes 1 kW of electric power when operated at 220 V. The minimum rating of the fuse wire to be used for it is

For a current in a long straight solenoid, N and S poles are created at the two ends. Among the following statements, the incorrect statement is :

Assertion (A) : In the following reaction $\mathrm{ZnO + C\longrightarrow Zn + CO}$. Reason (R) : Carbon is a reducing agent that reduces ZnO to Zn.

Assertion (A) : Human populations show a great deal of variations in traits. Reason (R) : All variations in a species have equal chances of surviving in the environment in which they live.

Assertion (A) : The walls of atria are thicker than those of the ventricles. Reason (R) : Ventricles have to pump blood into various organs at high pressure.

Assertion (A) : Two magnetic field lines around a current carrying straight wire do not intersect each other. Reason (R) : The magnitude of the magnetic field produced at a given point increases as the current through the wire increases.

(a) On heating $X'$ at $373\mathrm{K}$, it loses water molecules and becomes $Y'$. $Y'$ is a substance which doctors use for supporting fractured bones in the right position. (i) Identify $X'$ and $Y'$. (ii) How can $X'$ be reobtained from $Y'$? OR (b) Two solutions M and N give Red and Blue colour respectively with a universal indicator. (i) In which solution will the hydrogen ion concentration be more? Justify your answer. (ii) If both M and N solutions are mixed and the resultant mixture is tested with a universal indicator, it turns green. What is the nature of the salt formed? Justify your answer.

Write the name and function of parts (i) and (ii) in the diagram of a neuron given below.

(a) List the events in proper sequence that take place during the process of photosynthesis. OR (b) Explain in brief two ways by which leaves of a plant help in excretion.

In the process of digestion of food in human beings, two protein-digesting enzymes are secreted. Name the enzymes along with the glands that secrete them.

Observe the following diagram showing an image formation in an eye : (a) Identify the defect of vision shown in the figure. (b) List its two causes and suggest a suitable corrective lens to overcome this defect.

In the following food chain, if 50 J of energy was available to the hawk, how much energy would have been present at the first and third tropic levels? Justify your answer. Grass $\longrightarrow$ Grasshopper $\longrightarrow$ Frog $\longrightarrow$ Snake $\longrightarrow$ Hawk

(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.

(a) Sometimes the pH of our mouth gets lower than 5·5. Why? (b) A basic salt 'X' is obtained by heating baking soda followed by crystallisation. Identify 'X' and state its two industrial uses. (c) Why do copper sulphate crystals turn white on heating?

(a) With the help of an activity, explain the action of saliva on the food we eat. (b) Why is bile juice important in the process of digestion?

(a) (i) An object of $5\mathrm{cm}$ height is placed at a distance of $20\mathrm{cm}$ from the optical centre of a concave lens of focal length $18\mathrm{cm}$. Calculate (1) image distance and (2) the magnification in this case. (ii) Compare the values of magnification obtained by a concave lens and a convex lens when both the lenses form virtual images. OR (b) A convex lens can form a (i) real, inverted and magnified image as well as (ii) virtual, erect and magnified image of an object. If the focal length of the lens is $10\mathrm{cm}$, what should be the range of the object distance in both cases? Draw ray diagrams to justify your answer.

(a) State one important function of the following parts of the human eye: (i) Retina (ii) Pupil (b) State the role of ciliary muscles in focussing objects at varying distances from the eye.

(a) (i) A straight cylindrical conductor is suspended with its axis perpendicular to the magnetic field of a horse-shoe magnet. The conductor gets displaced towards left when a current is passed through it. What will happen to the displacement of the conductor if the (1) current through it is increased? (2) horse-shoe magnet is replaced by another stronger horse-shoe magnet? (3) direction of current through it is reversed? (ii) Name and state the rule for determining the direction of force on a current carrying conductor in a magnetic field. OR (b) Draw the pattern of the magnetic field produced around a vertical current carrying straight conductor passing through a horizontal cardboard. Mark the direction of current and the magnetic field lines. Name and state the rule which is used to determine the direction of magnetic field associated with a current carrying conductor.

How is ozone formed in the higher levels of the atmosphere? "Damage to the ozone layer is a cause of concern." Justify this statement.

(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

(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.

Metals are required for a variety of purposes. For this we need their extraction from their ores. Ores mined from the earth are usually contaminated with many impurities which must be removed prior to the extraction of metals. The extraction of pure metal involves the following steps: (1) Concentration of ore (2) Extraction of the metal from the concentrated ore (3) Refining of the metal (a) Name an ore of Mercury and state the form in which Mercury is present in it. (b) What happens to zinc carbonate when it is heated strongly in a limited supply of air? (c) The reaction of a metal A with $\mathrm{Fe}_2\mathrm{O}_3$ is highly exothermic and is used to join railway tracks. (I) Identify the metal A and name the reaction taking place. (II) Write the chemical equation for the reaction of metal A with $\mathrm{Fe}_2\mathrm{O}_3$. OR (c) We cannot use carbon to obtain sodium from sodium oxide. Why? State the reactions taking place at cathode and anode during electrolytic reduction of sodium chloride.

In some families, either rural or urban, females are tortured for giving birth to a female child. They do not seem to understand the scientific reason behind the birth of a boy or a girl. In fact the mother is not responsible for the sex of the child and it has been genetically proved that the sex of a newborn is determined by what the child inherits from the father. (a) State the basis on which the sex of a newborn baby is determined in humans. (b) Why is the pair of sex chromosomes called a mismatched pair in males? (c) How is the original number of chromosomes present in the parents restored in the progeny? OR (c) Explain by giving two examples of the organisms in which the sex is not genetically determined.

Many optical instruments consist of a number of lenses. They are combined to increase the magnification and sharpness of the image. The net power (P) of the lenses placed in contact is given by the algebraic sum of the powers of the individual lenses $\mathrm{P}_1, \mathrm{P}_2, \mathrm{P}_3 \ldots$ as $\mathrm{P} = \mathrm{P}_1 + \mathrm{P}_2 + \mathrm{P}_3\ldots$ This is also termed as the simple additive property of the power of lens, widely used to design lens systems of cameras, microscopes and telescopes. These lens systems can have a combination of convex lenses and also concave lenses. (a) What is the nature (convergent / divergent) of the combination of a convex lens of power $+4 \mathrm{D}$ and a concave lens of power $-2 \mathrm{D}$ ? (b) Calculate the focal length of a lens of power $-2 \cdot 5 \mathrm{D}$ . (c) Draw a ray diagram to show the nature and position of an image formed by a convex lens of power $+0 \cdot 1 \mathrm{D}$ , when an object is placed at a distance of $20 \mathrm{cm}$ from its optical centre. OR (c) How is a virtual image formed by a convex lens different from that formed by a concave lens? Under what conditions do a convex and a concave lens form virtual images?