The lowest freezing point is given by the solute which has highest depression in freezing point. Depression in freezing point is a colligative property which depends upon the number of ions. Depression in freezing point ∝ number of molecules or ions. In given alternatives only CaCl2 gives maximum number of ion (3 ions). So, it has maximum depression in freezing point. Therefore, 0.1mCaCl2 solution has lowest freezing point.