# One mole of two different compounds happens to weight the same, but one compound ionizes in water and the other does not. Which will give the lowest freezing point depression?

A binary ionic species, $M X$, will give rise to two species in solution, i.e:
$M X \left(s\right) \rightarrow {M}^{+} \left(a q\right) + {X}^{-} \left(a q\right)$
The ions are aquated by several water molecules, and are hence represented as ${M}^{+} \left(a q\right)$. And since $\text{freezing point depression}$ is a colligative property that depends on the number of particles in solution, the binary salt will give TWICE the freezing point depression of a neutral solvate.