Smaller the size of an ion, greater will be the degree of hydration. So, degree of hydration is highest for Li⁺ and that is smallest for Cs⁺. Therefore, Li⁺ holds the water molecules in its hydration sphere and Cs⁺ ion holds the least water molecules.

Hence, the correct ionic mobility in aqueous medium is :

Cs⁺ > Rb⁺ > K⁺ > Na⁺

The stability of alkali metal hydrides decreases from Li to Cs. It is due to the fact that M–H bonds becomes weaker with increase in size of alkali metals as we move down the group from Li to Cs. Thus the order of stability of hydrides is

LiH > NaH > KH > RbH > CsH

Equimolar solutions of the given chlorides when prepared in water forms their respective hydroxides.

SrCl₂ + 2H₂O $$ \to $$ Sr(OH)₂ + 2HCl

BaCl₂ + 2H₂O $$ \to $$ Ba(OH)₂ + 2HCl

MgCl₂ + 2H₂O $$ \to $$ Mg(OH)₂ + 2HCl

CaCl₂ + 2H₂O $$ \to $$ Ca(OH)₂ + 2HCl

Be(OH)₂ is amphoteric, but the hydroxides of other alkaline earth metals are basic. The basic strength increases down the group. Hence higher the basic character higher will be the pH.

Hydration energy of sulphate decreases on moving down the group-II. Mg²⁺ is smaller than other ions of group II, so Mg²⁺ is readily hydrated and hence MgSO₄ has higher hydration energy than the lattice energy.