dereasing order of electron gain enthalpy of group18

Electron gain enthalpy is the energy associated with the addition of one electron to a neutral atom. Inert gases have completely filled orbital and so they have highest energy among all other groups. In a group as the size increases the energy decreases. But due to its very smaller size He has the lowest energy. That is why the order is
Ne > Ar= Kr > Xe > Rn > He