Under similar conditions, which halide ion is the best reducing agent?

• A. Fluoride ion
• B. Iodide ion
• C. Chloride ion
• D. Bromide ion

Answer: (B)

Reducing power comes from how readily a species loses electrons. For halide ions, losing electrons means being oxidized to the corresponding halogen, and this tendency increases as you move down the group. The I2/I– couple has the smallest standard reduction potential among the halogens shown (about +0.54 V), meaning the reverse oxidation (I– to I2) is comparatively easy. Hence iodide donates electrons more readily than bromide or chloride, making it the strongest reducing agent under similar conditions. Fluoride’s F2/F– pair has a much higher reduction potential (+2.87 V), so fluoride is not oxidized as easily and is a weaker reducing agent than iodide.