Chemistry - Halogen Derivative Question with Solution | TestHub

The provided order ($R-I>R-Br>R-Cl>R-F$) represents the relative reactivity of alkyl halides based on leaving group ability.

In all four mechanisms ($S_{N}1$, $S_{N}2$, $E1$, and $E2$), the carbon-halogen ($C-X$) bond breaks during the rate-determining step.

Leaving group ability increases as the $C-X$ bond strength decreases: $I^{-}$ is the best leaving group because the $C-I$ bond is the weakest and easiest to break.

Additionally, $I^{-}$ is the most stable conjugate base (weakest base), further facilitating its departure compared to $F^{-}$.

Since a better leaving group accelerates any reaction where the $C-X$ bond must break, the trend is valid for both substitution and elimination pathways.

Consequently, the order is correct for all given options: (A), (B), (C), and (D).