Question

Which of the following has least bond dissociation energy ?

• A. ${\mathrm{F}}_2$
• B. ${\mathrm{Cl}}_2$
• C. ${\mathrm{I}}_2$
• D. ${\mathrm{Br}}_2$

Answer 1

The correct option is C

${\mathrm{I}}_2$

Explanation for the correct option:

(c ) ${\mathrm{I}}_2$

• Order of bond dissociation:
• ${\mathrm{Cl}}_2>{\mathrm{Br}}_2>{\mathrm{F}}_2>{\mathrm{I}}_2$
• ${\mathrm{I}}_2$ has the least bond dissociation energy due to its largest size.
• Hence this option is correct

Explanation for the incorrect options:

(a) ${\mathrm{F}}_2$

• Fluorine's lower bond dissociation energy is related to the strong inter-electronic repulsion amongst non-bonding electrons in its 2p-orbitals.
• As a result, the $\mathrm{F}-\mathrm{F}$ bond is weaker than the ${\mathrm{I}}_2$ bonds.
• Thus, this option is incorrect.

(b) ${\mathrm{Cl}}_2$

• The $\mathrm{Cl}-\mathrm{Cl}$ bond is weaker than the $\mathrm{Br}-\mathrm{Br}$ bonds.
• Thus, this option is incorrect.

(d) ${\mathrm{Br}}_2$

• The $\mathrm{Br}-\mathrm{Br}$ bond is weaker than the ${\mathrm{I}}_2$ and $\mathrm{F}-\mathrm{F}$ bonds.
• Thus, this option is incorrect.

Hence the correct option is (c ) ${\mathrm{I}}_2$