Question

In the reaction, ${\mathrm{Br}}_2+2{\mathrm{I}}^{-}\to 2{\mathrm{Br}}^{-}+{\mathrm{I}}_2$, the oxidizing agent is-

• A. ${\mathrm{Br}}_2$
• B. ${\mathrm{I}}^{-}$
• C. $\mathrm{Br}$
• D. ${\mathrm{I}}_2$

Answer 1

The correct option is A

${\mathrm{Br}}_2$

Explanation of the correct option (Option A):

1. Oxidation is defined as the gain of an oxygen atom ($\mathrm{O}$) or the loss of electrons.
2. Reduction is defined as the loss of an oxygen ($\mathrm{O}$) atom or gain of a hydrogen ($\mathrm{H}$) atom or the gain of electrons.
3. An oxidizing agent is a substance that oxidizes other substances by gaining electrons and a reducing agent is a substance that reduces other substances by donating electrons.
4. Half reaction: The two half-reactions showing oxidation and reduction in the given reaction are: $$\begin{gathered} \mathrm{Oxidation}:2{\mathrm{I}}^{-}\left(\mathrm{aq}\right)\to {\mathrm{I}}_2\left(\mathrm{s}\right)+2{\mathrm{e}}^{-} \\ \mathrm{Iodide}\mathrm{ion}\mathrm{Iodine} \\ \mathrm{Reduction}:{\mathrm{Br}}_2\left(\mathrm{l}\right)+2{\mathrm{e}}^{-}\to 2{\mathrm{Br}}^{-}\left(\mathrm{aq}\right) \\ \mathrm{Bromine}\mathrm{Bromide}\mathrm{ion} \end{gathered}$$
5. As Bromine (${\mathrm{Br}}_2$) is gaining electrons, thus it is undergoing reduction and it is behaving as an oxidising agent.

Explanation of the incorrect options-

B) ${\mathbf{I}}^{\mathbf{-}}$: ${\mathrm{I}}^{-}$ion has extra electrons so it will lose electrons and get reduced to ${\mathrm{I}}_2$. Hence it is a strong reducing agent.

C) $\mathbf{Br}$: Single bromine atom is not available in a stable state.

D) ${\mathbf{I}}_{\mathbf{2}}$: ${\mathrm{I}}_2$ is formed by the oxidation of ${\mathrm{I}}^{-}$, where ${\mathrm{I}}^{-}$ ion loses electrons when ${\mathrm{Br}}_2$ is added to the solution. Hence, it is a reducing agent.

Hence the correct option is A, ( ${\mathbf{Br}}_{\mathbf{2}}$).