Inert gases have positive electron gain enthalpy. Its correct order is

Inert  gases have stable electronic configuration. Therefore, some external energy is needed (endothermic,  $\Delta H>0$) to add the electron in their subshell. Hence, electron gain enthalpy for inert gases will be positive.
   The values of electron gain enthalpy in $KJ/mol$ for  $He,Ne,Ar,Kr,Xe$ are $+48,+116,+96$ and $+77$respectively.
   Hence, the correct order of positive electron gain enthalpy is $He<Xe<Kr<Ne$