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JEE Main levelSingle correct optionDifficulty 2 of 3so067

Two solutes P (molar mass $60 g mo l^{- 1}$ ) and Q (molar mass $180 g mo l^{- 1}$ ), both non-electrolytes, are dissolved separately, $6.0 g$ each, in $100 g$ of water. The ratio $Δ T_{f} (P) : Δ T_{f} (Q)$ is

A $9 : 1$
B $1 : 1$
C $3 : 1$
D $1 : 3$

Answer: C

For the same mass of solvent,

Δ T_{f} \propto

moles of solute

= w / M

. Moles of P

= 6/60 = 0.10

and moles of Q

= 6/180 = 0.033

, so the ratio is

0.10/0.033 = 3

, i.e.

3 : 1

.

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