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

B r_{2} > I_{2} > F_{2} > C l_{2}

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F_{2} > C l_{2} > B r_{2} > I_{2}

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I_{2} > B r_{2} > C l_{2} > F_{2}

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C l_{2} > B r_{2} > F_{2} > I_{2}

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Solution

The correct option is D $C l_{2} > B r_{2} > F_{2} > I_{2}$
The order of bond dissociation enthalpy is :
$C l_{2} > B r_{2} > F_{2} > I_{2}$

As you go down the group the bond dissociation enthalpy should decrease, the only anomaly being Fluorine due to its small size.
Two fluorine atoms must come together to share a pair, but these many electrons concentrated on two small nuclei and separated over comparatively a very small distance repel each other.

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