Question

Among the halide ions, the most powerful reducing agent is:

• A. $C{l}^{-}$
  
• B. $I^{-}$
  
• C. $B{r}^{-}$
• D. $F^{-}$

Answer 1

Answer: (B)

$I^{-}$

Of the halide ion, $I^{-}$ is the most powerful reducing agent.
The standard reduction potentials for $F^{-}|F_2|Pt$, $C{l}^{-}|C{l}_2|Pt$, $B{r}^{-}|B{r}_2|Pt$ and $I^{-}|I_2|Pt$ electrodes are $+2.87$ V, $+1.36$ V, $+1.08$ V and $+0.535$ V respectively.
Thus, $I^{-}|I_2|Pt$ electrode has lowest value of standard reduction potential. As the standard reduction potential value decreases, the reducing power increases.