Q23 / 90 · JEE Main 2022 (29 Jun Shift 2) · Chemistry

Elevation in boiling point for $1.5$ molal solution of glucose in water is $4 K$ . The depression in freezing point for $4.5$ molal solution of glucose in water is $4 K$ . The ratio of molal elevation constant to molal depression constant $(K_{b} / K_{f})$ is

Correct answer: 3

Solution

Elevation in boiling point $∆ T_{b} = {ik}_{b} m_{1}$

Depression in freezing point $∆ T_{f} = {ik}_{f} m_{2}$

$4 = {ik}_{b} (1.5)$

$4 = {ik}_{f} (4.5)$

Dividing both:

$\frac{k_{b}}{k_{f}} = \frac{3}{1}$

Hence, The ratio of molal elevation constant to molal depression constant is 3:1

Hence, the correct answer is 3.