. In which of the following options the order of arrangement
does not agree with the variation of property indicated against it?
(a) I < Br < Cl < F (increasing electron gain enthalpy)
(b) Li < Na < K < Rb (increasing metallic radius)
(c) Al3+ < Mg2+ < Na+ < F- (increasing ionic size)
(d) B < C < N < O (increasing first ionization enthalpy
Correct Option is: A, B
Because of higher change density and electron-electron repulsion in tiny sized F atoms, the proper order of increasing negative electron gain enthalpy is I < Br < F < Cl, and the correct order of rising first ionisation enthalpy is B < C < O < N because of the increased stability of half-filled orbitals in the N-atom.
Note: Similar abnormal trend is observed in electron affinity in case of Oxygen and Sulphur. Where electron affinity of S > O.