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

Question

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

0.56 K