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

Noble (inert) gases have positive electron gain enthalpy. They possess completely filled and highly stable electron configurations: He (1s$$^2$$), Ne (2s$$^2$$2p$$^6$$), Ar (3s$$^2$$3p$$^6$$), Kr (4s$$^2$$4p$$^6$$), Xe (5s$$^2$$5p$$^6$$). Adding an extra electron would place it in the next higher principal shell, which is energetically very unfavourable; therefore, the process of electron addition is endothermic (positive electron gain enthalpy).

As we move down the group from He to Xe, the atomic size increases, so the next available shell is farther from the nucleus; the shielding effect increases, making it progressively more difficult to stabilise the incoming electron; and the incoming electron must enter an increasingly higher energy level (n = 2 for He, n = 3 for Ne, n = 4 for Ar, etc.), all of which make the electron gain enthalpy more positive. Therefore, the positive electron gain enthalpy increases as we go down the group.

In increasing order of positive electron gain enthalpy: $$\text{He} < \text{Ne} < \text{Kr} < \text{Xe}$$. He has the least positive electron gain enthalpy and Xe has the most positive.

Answer: Option B