Which element of group-$1$ has the highest hydration enthalpy? Why?

(A) Among the group-$1$ elements,$Li^+$ ion has the highest hydration enthalpy.
This is because the hydration enthalpy depends on the size of the ion.
Smaller ions have a higher charge density,which allows them to attract water molecules more strongly.
Since $Li^+$ is the smallest ion in group-$1$,it has the highest charge density and thus the highest hydration enthalpy.