Assertion and Reason

Matter in Our Surroundigs

Assertion and Reason type Questions of Chapter 1 of Science of Class 9th.

DIRECTION : In the following questions, a statement of assertion (A) is followed by a statement of reason (R). Mark the correct choice as:

(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
(c) Assertion (A) is true but reason (R) is false.
(d) Assertion (A) is false but reason (R) is true.

(1). Assertion : The term vapour is used to represent the gaseous state of a substance which is otherwise liquid at room temperature.
Reason : It is proper to regard the gaseous state of ammonia as vapours.

(c) Assertion (A) is true but reason (R) is false.

Explanation: It is not proper to regard ammonia in gaseous state as vapour because ammonia is not liquid at room temperature.

(2). Assertion : Camphor disappears without leaving any residue.
Reason : Camphor undergoes sublimation.

(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).

(3). Assertion : Naphthalene does not leave any residue when kept open for some time.
Reason : The conversion of a solid directly into gas is called condensation.

(c) Assertion (A) is true but reason (R) is false.
Explanation: The conversion of a solid directly into gas is called sublimation.

(4). Assertion : It is easier to cook food at high altitudes.
Reason : The boiling point of water increases at high altitudes.

(d) Assertion (A) is false but reason (R) is true.

Expalnation: It is difficult to cook food at high altitudes since the boiling point of water decreases at high altitudes and it does not provide sufficiently high temperature to the food to get cooked.

(5). Assertion : During evaporation of liquids, the temperature remains unaffected.
Reason : Kinetic energy of the molecules is inversely proportional to absolute temperature.

(d) Assertion (A) is false but reason (R) is true.

Explanation: During evaporation of liquids, the temperature decreases due to escape of molecules with high energy.
Kinetic energy of the molecules is directly proportional to absolute temperature.

(6). Assertion : Naphthalene, camphor, iodine, ammonium chloride are some common examples of the substances which undergo sublimation.
Reason : All solids are first converted to liquids and then to gases on heating.

(c) Assertion (A) is true but reason (R) is false.

Explanation: Certain solids directly change to the gaseous state upon heating without passing through the liquid state. This process is called sublimation.

(7). Assertion : Ice floats on the surface of water.
Reason : The density of both water and ice is same.

c) Assertion (A) is true but reason (R) is false.

Explanation: Ice floats of the surface of water because the density of water is more than ice. Ice is lighter than water due to open spaces in its crystalline structure.

(8). Assertion : There is no change in the temperature of a substance when it undergoes a change of state through it is still being heated.
Reason : The heat supplied is absorbed either as latent heat of fusion or as latent heat of vaporisation.

(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).

Explanation: The heat supplied during the state transformation does not increase the kinetic energy but is absorbed for conversation of complete solid to liquid or complete liquid to vapours.

(9). Assertion : Solids do not diffuse in air.
Reason : The particles are closely packed in solids.

(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).

Explanation: As the particles of solids are closely packed, there exist strong forces of attraction between the particles. Hence, solids do not diffuse in air.

(10). Assertion : The conversion of a gas directly into solid is called condensation.
Reason : Naphthalene leaves residue when kept open for some time.

(d) Assertion (A) is false but reason (R) is true.

Explanation: The conversion of a gas directly into solid is called desublimation. Naphthalene does not leave any residue when kept open for some time.

(11). Assertion : Liquids diffuse less easily as compared to gases.
Reason : Intermolecular forces are greater in gases.

(c) Assertion (A) is true but reason (R) is false.

Explanation: Liquids diffuse slowly as compared to gases. Liquids have stronger intermolecular forces as compared to gases hence liquid molecules are less free to move than gases.

(12). Assertion : At normal pressure (1 atm) the boiling point of water is 1000 C or 373.15 K.
Reason :  As the pressure increases, boiling point of water also increases.

(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).

(13). Assertion : The rate of evaporation increases with increase in temperature.
Reason : Increase in temperature increases the kinetic energy of the particles.

(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).

Explanation: Increase in temperature increases the kinetic energy of the particles, as a result of which more and more particles escape from liquid to vapour state.

(14). Assertion : Naphthalene, camphor, iodine, ammonium chloride are some common examples of the substances which undergo sublimation.
Reason : All solids are first converted to liquids and then gases on heating.

(c) Assertion (A) is true but reason (R) is false.

Explanation: Certain solids directly change to the gaseous state upon heating without passing through the liquid state. The process is called sublimation.

(15). Assertion : The intermolecular forces in solid state are stronger than those in the liquid state.
Reason : The space between the particles of matter is called intermolecular space.

(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).

(16). Assertion : Liquids diffuse easily as compared to gases.
Reason : Intermolecular forces are greater in gas.

(d) Assertion (A) is false but reason (R) is true.

Explanation: Liquids diffuse slowly as compared to gases, Liquid molecules are less free to move because intermolecular forces in liquids are greater than in gases.

(17). Assertion : Ice floats on the surface of water.
Reason : The density of both water and ice is same.

(c) Assertion (A) is true but reason (R) is false.

Explanation: Ice floats on the surface of water because the density of water is more than ice. Ice is lighter than water due to open spaces in its crystalline structure.

(18). Assertion : Diffusion rate of oxygen is smaller than nitrogen.
Reason : Molecular size of nitrogen is smaller than oxygen.

(c) Assertion (A) is true but reason (R) is false.

Explanation: Diffusion rate of oxygen is smaller than nitrogen as molecular mass of oxygen is greater than nitrogen, as diffusion rate `\alpha \frac{1}{\sqrt{M}}`.
Molecular size of oxygen is smaller than nitrogen.

(19). Assertion : A gas can be easily compressed by applying pressure.
Reason : Since the inter-particle spaces in the gaseous state are very small, they cannot be decreased by applying pressure.

(c) Assertion (A) is true but reason (R) is false.

Explanation: Since the inter-particle spaces in the gaseous state are very large, they can be decreased by applying pressure. Thus, a gas can be easily compressed by applying pressure.

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