Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R) Assertion (A) : At $10^{\circ} \mathrm{C}$, the density of a 5 M solution of KCl [atomic masses of K and Cl are 39 $\& 35.5 \mathrm{~g} \mathrm{~mol}^{-1}$]. The solution is cooled to $-21^{\circ} \mathrm{C}$. 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:

(A) Both (A) and (R) are true and (R) is the correct explanation of (A)

(B) Both (A) and (R) are true but (R) is not the correct explanation of (A)

(C) (A) is true but (R) is false

(D) (A) is false but (R) is true

JEE Main · 2022 · 27 Jun 2022 · Shift 1 · Solutions

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R)

Assertion (A) : At

1 0^{\circ} C

, the density of a 5 M solution of KCl [atomic masses of K and Cl are 39

&35.5 g mol^{- 1}

]. The solution is cooled to

- 2 1^{\circ} 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:

(A)Both (A) and (R) are true and (R) is the correct explanation of (A)✓ Correct
(B)Both (A) and (R) are true but (R) is not the correct explanation of (A)
(C)(A) is true but (R) is false
(D)(A) is false but (R) is true

Answer: (A)

Solution

Molality is defined as moles of solute per kilogram of solvent. Since both mass of solute and mass of solvent remain constant with temperature change, molality is independent of temperature. Therefore, both the assertion and reason are true, and the reason correctly explains the assertion.

JEE Main · 2022 · 27 Jun 2022 · Shift 1 · Single correct option

Practise more: all JEE Main PYQs on Solutions →

JEE Main · 2022 · 27 Jun 2022 · Shift 1 · Solutions

Solution

More JEE Main questions on Solutions