Which one of the following orders is correct for the bond dissociation enthalpy of halogen molecules ?

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F₂ > Cl₂ > Br₂ > I₂

Br₂ > I₂ > F₂ > Cl₂

I₂ > Br₂ > Cl₂ > F₂

Cl₂ > Br₂ > F2 > I2

answer is D.

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Detailed Solution

Bond lengths of halogens are in the order : F₂ < Cl₂ < Br₂ < I₂.
Bond energies are expected in the order :F₂ > Cl₂ > Br₂ > Cl₂.
But the experimental bond enthalpies are :Cl₂ > Br₂ > F₂ > I₂ Bond enthalpy of F₂ is very less, because lone pair - lone pair repulsions are appreciable in F₂ as the bond length is small in F₂. It was also thought, though not appropriate, that F–F bond is weak as multiple bond is not possible with no d-orbitals in the valence shell of fluorine.