Question

Assertion: At 10°C, the density of 5 M solution of KCl [atomic masses of K and Cl are 39 and 35.5 g mol⁻¹]. The solution is cooled to −21°C. The molality of solution will remain unchanged.

Reason: The molality of a solution does not change with temperature as mass remains unaffected with temperature.

Options

• If both Assertion and Reason are CORRECT and Reason is the CORRECT explanation of the Assertion.

• If both Assertion and Reason are CORRECT but Reason is not the CORRECT explanation of the Assertion.

• If Assertion is CORRECT but Reason is INCORRECT.

• If Assertion is INCORRECT but Reason is CORRECT.

Answer 1

If both Assertion and Reason are CORRECT and Reason is the CORRECT explanation of the Assertion.

Explanation:

Molality is defined as the number of moles of solute per kilogram of solvent and does not depend on volume. Since mass is independent of temperature, cooling the solution from 10°C to –21°C will not affect the molality. Hence, both the assertion and reason are correct, and the reason correctly explains the assertion.