Question

Of the following 0.1 M aqueous solutions, which one will exhibit the largest freezing point depression?

• A. $A{l}_2(S{O}_4{)}_3$
• B. $KCl$
• C. $K_{2}S{O}_4$
• D. $C_6{H}_{12}{O}_6$

Answer 1

The correct option is A $A{l}_2(S{O}_4{)}_3$

Depression in freezing point is given by,
$△T_f=i\times K_f\times m$
where,
$△T_f$ is the depression in freezing point.
$K_f$ is molal depression constant.
m is molality of solution.
i is van't Hoff factor

Molality of all given solutions are same, hence,
$\text{Depression in freeziong point}\propto i$

$K_{2}S{O}_4\to 2K^{+}\left(aq\right)+S{O}_4^{2-}\left(aq\right)$
$i=3$

$KCl\to K^{+}+C{l}^{-}$
$i=2$

$A{l}_2(S{O}_4{)}_3\to 2A{l}^{3+}+3S{O}_4^{2-}$
$i=5$

$i$ for $C_6{H}_{12}{O}_6$ is 1

Hence, option (c) is correct.