Affinity for hydrogen decreases in the group from fluorine to iodine. Which of the halogen acids should have highest bond dissociation enthalpy?

BOND DISSOCIATION ENTHALPY: bond dissociation enthalpy is defined as the energy required to break the bonds between two atoms.

With increase in bond length, bond dissociation enthalpy decreases because bond of large length is easy to break than bond of smaller length. Larger amount of energy is required to break the small bond while very less amount of energy is required to break large bond.

Thus bond dissociation enthalpy is inversely proportional to bond length.

As we move from HF to HI the bond length increases and bond dissociation enthalpy decreases down the halides.

Hence the correct option is (i).