Give brief information on Ionization Enthalpy and Hydration Enthalpy of alkali metal (Group $I$).

(N/A) The ionization enthalpies of the alkali metals are considerably low and decrease down the group from $Li$ to $Cs$. This is because the effect of increasing size outweighs the increasing nuclear charge,and the outermost electron is very well screened from the nuclear charge.
The hydration enthalpies of alkali metal ions decrease with an increase in ionic size.
$Li^{+} > Na^{+} > K^{+} > Rb^{+} > Cs^{+}$
$Li^{+}$ has the maximum degree of hydration,and for this reason,lithium salts are mostly hydrated,e.g.,$LiCl \cdot 2H_{2}O$.