Freezing Point Questions

$0.5\text{ molal}$ aqueous solution of a weak acid ($\text{HX}$) is $20\%$ ionised. If $K_f$ for water is $1.86{\text{ K kg mol}}^{-1}$, the lowering in freezing point of the solution is:

A solution of sucrose (molar mass $=342{\text{g mol}}^{-1}$) has been prepared by dissolving $68.5\text{g}$ of sucrose in $1000\text{g}$ of water. The freezing point of the solution obtained will be ($K_f$ for water $=1.86{\text{K kg mol}}^{-1}$):