Classification of Elements and Periodicity in Properties — Chemistry STD 11 Science — Question

Out of F(1s² 2s² 2p⁵), O(1s² 2s² 2p⁴), N(1s² 2s² 2p³) and S(1s² 2s² 2p⁶ 3s² 3p⁴), only N has positive electron gain enthalpy because of its stable exactly half-filled electronic configuration while all others have negative electron gain enthalpies. Since, F needs only one more electron to acquire the nearest inert gas configuration, therefore, it has the most negative electron gain enthalpy. Out of O and S, O has less negative electron gain enthalpy than S because of electron-electron repulsions present in its small compact 2p-orbital. Thus, overall order of increasing electron gain enthalpy is: (i) < (iv) < (ii) < (iii).