Question

Assertion: Molality is independent of temperature.
Reason: Volume of solution does not change with temperature.

• A. Both assertion and reason are correct and reason is the correct explanation for assertion.
• B. Both assertion and reason are correct but reason is not the correct explanation for assertion.
• C. Assertion is correct but the reason is incorrect.
• D. Both assertion and reason are incorrect.

Answer 1

The correct option is C

Assertion is correct but the reason is incorrect.

Explanation for correct option:

Assertion:-

• Molality is the measure of the number of moles of solute in a solution corresponding to mass of solvent:

$\mathrm{Molality}=\frac{\mathrm{number}\mathrm{of}\mathrm{moles}\mathrm{of}\mathrm{the}\mathrm{solute}}{\mathrm{mass}\mathrm{of}\mathrm{the}\mathrm{solvent}\mathrm{in}\mathrm{kg}}$

• Here the number of moles of solute and mass of the solvent both are not dependent on temperature, that is they are temperature independent.
• Hence molality is temperature independent.
• Thus the assertion is true.

Explanation for reason:-

• Volume is directly proportional to the temperature.
• More the temperature is more will be the volume.
• This is because, as the temperature increases, the kinetic energy of the molecules in the gas also increases.
• As a result they vibrate even more and move further away from each other.
• Thus resulting in the increase of the volume of the gas.
• Thus the reason is false.

Therefore, option (C) Assertion is correct but the reason is incorrect, is the correct answer.