The freezing point of a solution containing 36g of a compound (empirical formula : $CH_2O$) in 1.20 kg of water is found to be $-0.93^{\large\circ}C$.The molecular formula of the solute is

Question

$\begin{array}{1 1}CH_2O\\C_2H_4O_2\\C_3H_6O_3\\C_4H_8O_4\end{array} $