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JEE Main levelSingle correct optionDifficulty 2 of 3ph012

The bond dissociation enthalpy of $F X_{2}$ (158.8 kJ/mol) is lower than that of $Cl X_{2}$ (242.6 kJ/mol) mainly because

Afluorine uses vacant $3 d$ orbitals to form a weaker pi bond
Bfluorine is less electronegative than chlorine
Cthe F-F bond is longer than the Cl-Cl bond
Dstrong repulsion between the lone pairs on the two small fluorine atoms weakens the F-F bond

Answer: D

The F-F bond is very short, so the three lone pairs on each F atom repel strongly and weaken the bond. Fluorine is the most electronegative halogen, its bond is shorter than Cl-Cl, and it has no

d

orbitals, so the other reasons are wrong.

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