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Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): At 10°C, the density of a 5 M solution of KCl [atomic masses of K & Cl are 39 & 35.5 g mol−1 respectively], is ‘x’ g mL−1. The solution is cooled to −21°C. The molality of the solution will remain unchanged. Reason (R): The molality of a solution does not change with temperature as mass remains unaffected with temperature. In the light of the above statements, choose the correct answer from the options given below. (1) Both (A) and (R) are true and (R) is the correct explanation of (A). (2) Both (A) and (R) are true but (R) is not the correct explanation of (A). (3) (A) is true but (R) is false. (4) (A) is false but (R) is true.

1. Both (A) and (R) are true and (R) is the correct explanation of (A).
2. Both (A) and (R) are true but (R) is not the correct explanation of (A).
3. (A) is true but (R) is false.
4. (A) is false but (R) is true.

Correct answer: Both (A) and (R) are true and (R) is the correct explanation of (A).

Solution

Both statements are accurate because the density of the solution at 10°C is relevant to its properties, and as the temperature decreases, the mass of the solute and solvent remains constant, thus keeping the molality unchanged. Therefore, the reason correctly explains why the assertion holds true.

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