EXPLANATION

Electron gain enthalpy of elements having fully filled orbitals will be extremely positive as they do not want to lose their stability. So in the first case it is +48kJmol^-1. In the second case s orbital has just one electron so this element has more tendency to donate electron but as it can also gain one electron to complete its s orbital so it has a low negative electron gain enthalpy. In the third case just one electron is required to fill the p orbital. Hence it has a very high negative electron gain enthalpy. In the fourth case as 2 more electrons are required so it has a negative electron gain enthalpy but it is less negative than the third case.