Answer: Iodide (C-I).
- A Fluoride (C-F)
- B Chloride (C-Cl)
- C Bromide (C-Br)
- D Iodide (C-I)
Correct answer: D. Iodide (C-I)
Explanation: Reactivity in nucleophilic substitution: RI > RBr > RCl > RF. C-I bond is weakest and iodide is the best leaving group due to its large, polarisable nature.
SN2 proceeds in a single step with backside attack and inversion of configuration, while SN1 forms a planar carbocation intermediate first, leading to racemisation.
Concept context
Study carbon-halogen compounds: how they are made, how they react via SN1/SN2 and elimination, their stereochemistry, and their environmental impact.