Q80 / 180 · AIIMS 2011 · Chemistry
Assertion : Chlorine undergoes disproportionation reaction in alkaline medium.
Reason : $\mathrm{Cl}_2$ is an oxidising agent.
- AIf both assertion and reason are true and reason is the correct explanation of assertion.
- Correct answerBIf both assertion and reason are true but reason is not the correct explanation of assertion.
- CIf assertion is true but reason is false.
- DIf both assertion and reason are false.
Solution
$$
\begin{aligned}
& \text { }: \mathrm{Cl}_2+2 \mathrm{NaOH} \text { (dil.) } \underset{\mathrm{cold}}{\longrightarrow} \\
& 3 \mathrm{Cl}_2+6 \mathrm{NaOH} \text { (conc.) } \underset{5 \mathrm{NaCl}}{\stackrel{\text { heat }}{\longrightarrow}}+\mathrm{NaOCl}+\mathrm{H}_2 \mathrm{O} \\
& \mathrm{NaClO}_3+3 \mathrm{H}_2 \mathrm{O}
\end{aligned}
$$
Chlorine undergoes the simultaneous oxidationreduction. Chlorine is simultaneously reduced to chloride ion $\left(\mathrm{Cl}^{-}\right)$and is oxidised to either $\mathrm{ClO}^{-}$ or $\mathrm{ClO}_3^{-}$ion. Halogens (e.g. Cl) have a strong tendency to accept electrons, so they act as strong oxidising agents.
Hence, the correct answer is option: 'B'.