. 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

Best Answer

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.

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