Question

Freezing point of a $4\%$ aqueous solution of $X$ is equal to freezing point of $12\%$ aqueous solution of $Y$. If molecular weight of $X$ is $A$, then molecular weight of $Y$ is:

• A. $A$
• B. $3A$
• C. $4A$
• D. $2A$

Answer 1

The correct option is B $3A$

For the same freezing point, molality of both solutions should be the same.

$m_x=m_y$

$\frac{4\times 1000}{96\times M_x}=\frac{12\times 1000}{88\times M_y}$

$M_y=\frac{96\times 12}{4\times 88}{M}_x=3.27A\approx 3A$

Hence, the correct option is $B$