$\mathbf{M X}_{\mathbf{2}}$ dissociates into $\mathbf{M}^{\mathbf{2 +}}$ and $\mathbf{X}$ - ions in an aqueous solution, with a degree of dissociation ( $\alpha$ ) of 0.5 . The ratio of the observed depression of freezing point of the aqueous solution to the value of the depression of freezing point in the absence of ionic dissociation is