Question

Which element undergoes disproportionation in water?

• A. $C{l}_2$
• B. $F_2$
• C. $K$
• D. $Cs$

Answer 1

Answer: (A)

The oxidation number of alkali metals ($K$ and $Rb$) is always $+1$.
Thus, these can not undergo disproportionation reaction.
Among halogens $C{l}_2,B{r}_2$ and $I_2$ can undergo disproportionation reaction but $F_2$ does not. The reason for this anomalous behaviour is that $Pa$ being the strongest oxidising agent does not show positive oxidation state.