Give reason: (a) F has lower electron gain enthalpy than Cl. (b) Ionization enthalpy of N is higher than O.
(a) Less negative electron gain enthalpy value of F is due to very small size of F atom. As a consequence of small size there are strong inter-electronic repulsions in relatively compact 2p- subshell of fluorine and thus electron does not feel much attraction. Cl is comparatively bigger in size than F and can accommodate electron easily. (b) Due to exactly half filled configuration of N [1s2 2s2 2px 1 2py 1 2pz 1] it is more stable than O [1s2 2s2 2px 2 2py 1 2pz 1]. So, ionization enthalpy of N is higher than O.