Answer
See the answer below.
Work Step by Step
Enthalpy of hydration is more negative with ions that are smaller and more positively charged:
A) LiCl, Lithium is the second period, Cs is the sixth
B) $Mg(NO_3)_2$ because magnesium is more positively charged.
C) $NiCl_2$ because nickel II is more positively charged.