MHTCET 19 Apr 2026 Shift 2 Paper

Concept:Bond dissociation enthalpy of halogens depends on bond length and lone-pair repulsion, not just atomic size.Explanation:Generally, bond enthalpy decreases down the group as atomic size increases and overlap weakens.So the expected order is $\mathrm{Cl}_{2} > \mathrm{Br}_{2} > \mathrm{I}_{2}$.But $\mathrm{F}_{2}$ is anomalous because its small atoms bring lone pairs very close, causing strong repulsion.This repulsion weakens the $\mathrm{F}-\mathrm{F}$ bond, making it weaker than $\mathrm{Cl}-\mathrm{Cl}$ and $\mathrm{Br}-\mathrm{Br}$.The actual bond dissociation enthalpies are:$\mathrm{Cl}_{2}: 243\ \mathrm{kJ\ mol}^{-1}$$\mathrm{Br}_{2}: 193\ \mathrm{kJ\ mol}^{-1}$$\mathrm{F}_{2}: 158\ \mathrm{kJ\ mol}^{-1}$$\mathrm{I}_{2}: 151\ \mathrm{kJ\ mol}^{-1}$Hence, the correct decreasing order is $\mathrm{Cl}_{2} > \mathrm{Br}_{2} > \mathrm{F}_{2} > \mathrm{I}_{2}$.Answer:Option C: $\mathrm{Cl}_{2} > \mathrm{Br}_{2} > \mathrm{F}_{2} > \mathrm{I}_{2}$