\mathrm{Rb}&\mathrm{Cs} have nearly same electron gain enthalpy Their values are nearly =−46kJ/mol
\mathrm{Ar}&\mathrm{Kr} also have same ΔHe.g.. Value is +96kJ/mol.
NaandK have different values (−53and−48kJ/mol). And IandAthasvaluesof−295and−270kJ/mol.
As we move down the group value of electron gain enthalpy decreases, with few exceptions.