a
As the size of the halogen atom increases from \(F\) to \(I, H-X\) bond length in halogen acids also increases from \(H-F\) to \(H I\).

\((H F \) to \(HI \) \( ( HF > HCl > HBr > HI )\)

Due to successive decrease in the strength of \(H X\) bonds, bonds dissociation enthalpy decreases from \(H F\) to \(H I\) \(H X\) Bond dissociation \(\underset{574.0}{H F}>\underset{428.1}{H C l}>\underset{362.5}{H B r}>\underset{294}{H I}\) enthalpy ( \(k J / m o l)\)