MHT CET Chemistry Question (2026) — Solution

Step-by-step solution

The bond dissociation enthalpy of halogens generally decreases down the group as the atomic size increases, which leads to less effective overlap of orbitals. However, the bond dissociation enthalpy of F _2 is exceptionally lower than that of Cl _2 and Br _2. This is due to the very small size of the fluorine atom, which results in strong interelectronic repulsions between the non-bonding electrons (lone pairs) on the two closely spaced fluorine atoms. The experimental values of bond dissociation enthalpies are approximately: Cl _2 = 242.6 kJ mol ^ -1 Br _2 = 192.8 kJ mol ^ -1 F _2 = 158.8 kJ mol ^ -1 I _2 = 151.1 kJ mol ^ -1 Thus, the correct decreasing order of bond dissociation enthalpy is Cl _2 > Br _2 > F _2 > I _2. Answer: Cl _2 > Br _2 > F _2 > I _2