Question

Consider the following redox reactions given below. Identify which of the following the example of a disproportionation reaction?

• A. $Cu+4HN{O}_3\to Cu(N{O}_3{)}_2+2N{O}_2+2H_{2}O$
• B. $3I_2+6O{H}^{-}\to I{O}_3^{-}+5I^{-}+3H_{2}O$
• C. $2ICl\to C{l}_2+I_2$
• D. $Zn+2HCl\to ZnC{l}_2+H_2$

Answer 1

The correct option is B $3I_2+6O{H}^{-}\to I{O}_3^{-}+5I^{-}+3H_{2}O$

Disproportionation reactions
The redox reaction in which an element from the same oxidation state changes to two different oxidation states (one lower and other higher)
(a)

$Cu$ is undergoing oxidation while $HN{O}_3$ is undergoing reduction, hence it is an intermolecular redox reaction.
(b)
$3I_2+6O{H}^{-}\to I{O}_3^{-}+5I^{-}+3H_{2}O$
here $I_2$ is undergoing oxidation as well as reduction.
So, this is a disproportionation reaction.
(c)

$I_2$ is undergoing oxidation while $C{l}_2$ is undergoing reaction. In this case, oxidation and reduction takes place through a single molecule so it is a intramolecular redox reaction.
d)
$Zn$ is undergoing oxidation while $HCl$ is undergoing reduction, hence it is an intermolecular redox reaction.