Q50 / 180 · NEET 2016 (Phase 1) · Chemistry

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

A
$I_{2} > B r_{2} > C l_{2} > F_{2}$
Correct answer
B
$C l_{2} > B r_{2} > F_{2} > I_{2}$
C
$B r_{2} > I_{2} > F_{2} > C l_{2}$
D
$F_{2} > C l_{2} > B r_{2} > I_{2}$

Solution

Decreasing order of Bond energy, $C l_{2} > B r_{2} > F_{2} > I_{2}$

The reason is anomalous behavior due to large electron - electron repulsion among the lone pairs in $F_{2}$ molecule other than $C l_{2}$ and $B r_{2}$ .

Hence, the correct answer is option: 'B'.

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