Question

Which of the following is not a disproportionate reaction?

• A. $4KCl{O}_3\to 3KCl{O}_4+KCl$
• B. $2C{u}^{+}\to C{u}^{2+}+Cu$
• C. $5X^{-}+X{O}_3^{-}+6H^{+}\to 3X_2+3H_{2}O$
• D. $4P+3NaOH+3H_{2}O\to P{H}_3+3Na{H}_{2}P{O}_2$

Answer 1

The correct option is C $5X^{-}+X{O}_3^{-}+6H^{+}\to 3X_2+3H_{2}O$

Disproportionation reaction are those in which same species oxidized and reduced simultaneously.
The change in oxidation numbers are
[a] $4K\stackrel{+5}{C}l{O}_3\to 3K\stackrel{+7}{C}l{O}_4+K\stackrel{-1}{C}l$
Cl : + 5 $\to$ +7 and -1
[b] $2\stackrel{+1}{C}{u}^{+}\to \stackrel{+2}{C}{u}^{2+}+\stackrel{+0}{C}u$
Cu : +1 $\to$ +2 and 0
[c] $5{\stackrel{-1}{X}}^{-}+\stackrel{+5}{X}{O}_3^{-}+6H^{+}\to 3{\stackrel{0}{X}}_2+3H_{2}O$
X : -1 $\to$ 0
[d] $4\stackrel{0}{P}+3NaOH+3H_{2}O\to \stackrel{-3}{P}{H}_3+3Na{H}_2\stackrel{+1}{P}{O}_2$
P : 0 $\to$ -3 and +1
In [a], [b] and [d], a single oxidation number (of the reactant atom) undergoes a simultaneous increase and decrease oxidation number hence it is both oxidising as well as reducing so they are disproportionation reaction, but in [c] two difference oxidation numbers of an atom in the reactants are not involved hence it is called as comproportionation reaction.