The difference between electron gain enthalpies will be maximum between :

Step-by-step solution

Electron gain enthalpy is defined as the amount of energy released when an electron is added to an isolated gaseous atom. During the addition of an electron, energy can either be released or absorbed. Electron gain enthalpy decreases down the group because as we move down the group, the size of an element increases, and the effective nuclear charge decreases. Due to this, the incoming electron will experience less attraction. Thus, electron gain enthalpy decreases as we move down the group. ΔH eg for chlorine