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Assertion : F - F bond has low bond dissociation energy.
Reason : The fluorine has lower reactivity.
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Reason : The fluorine has lower reactivity.
Solution:
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Verified Answer
The correct answer is:
If the assertion is true but the reason is false.
Lower value of bond dissociation energy of fluorine is due to the high inter electronic repulsions between non-bonding electrons of the $2 p$-orbital of small sized fluorine. As a result $\mathrm{F}-\mathrm{F}$ bond is weaker as comparison to $\mathrm{Cl}-\mathrm{Cl}$ and $\mathrm{Br}-\mathrm{Br}$ bonds.
$$
\begin{array}{lr}
& \text { Bond dissociation energy } \\
\mathrm{F}-\mathrm{F} & 38 \mathrm{~K} \mathrm{cal} / \mathrm{mole} \\
\mathrm{Cl}-\mathrm{Cl} & 57 \mathrm{~K} \mathrm{cal} / \mathrm{mole} \\
\mathrm{Br}-\mathrm{Br} & 45.5 \mathrm{~K} \mathrm{cal} / \mathrm{mole} \\
\mathrm{I}-\mathrm{I} & 35.6 \mathrm{~K} \mathrm{cal} / \mathrm{mole}
\end{array}
$$
$$
\begin{array}{lr}
& \text { Bond dissociation energy } \\
\mathrm{F}-\mathrm{F} & 38 \mathrm{~K} \mathrm{cal} / \mathrm{mole} \\
\mathrm{Cl}-\mathrm{Cl} & 57 \mathrm{~K} \mathrm{cal} / \mathrm{mole} \\
\mathrm{Br}-\mathrm{Br} & 45.5 \mathrm{~K} \mathrm{cal} / \mathrm{mole} \\
\mathrm{I}-\mathrm{I} & 35.6 \mathrm{~K} \mathrm{cal} / \mathrm{mole}
\end{array}
$$
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