(a,b,c) The hydration enthalpies of alkaline earth metal ions decrease with increase in ionic size down the group.

Be 2+ > Mg 2+ > Ca 2+ > Sr 2+ > Ba 2+

The hydration enthalpies of alkaline earth metal ions are larger than those of alkali metal ions, because of their much larger charge to radius ratio, exert a much stronger electrostatic attraction on the oxygen of water molecule surrounding them. Thus, compounds of alkaline earth metals are more extensively hydrated than those of alkali metals, e.g., MgCl 2 and CaCl 2 exist as MgCl 2 .6H 2 O and CaCl 2 . 6H 2 O while NaCl and KCl do not form such hydrates. So all statements are correct.