Question

Which of the following represents a disproportionation reaction?

• A. $N_{2(g)}+O_{2(g)} \to 2NO_{(g)}$
• B. $pb\left(NO_{3}\right)_{2\left(s\right)} \rightarrow pbO_{\left(s\right)}+2NO_{2\left(g\right)}+1/ 2O_{2\left(g\right)}$
• C. $NaH_{\left(s\right)}+H_{2}O_{\left(l\right)} \rightarrow NaOH_{\left(aq\right)}+H_{2}\left(g\right)$
• D. $2NO_{2\left(g\right)}+2OH_{\left(aq\right)}^{-}\rightarrow NO_{2\left(aq\right)}^{-}+NO_{3\left(aq\right)}^{-}+H_{2}O_{\left(l\right)}$

Answer 1

Answer: (D)

(a) $\overset{0}{N}_{2(g)}+\overset{0}{O}_{2{(g)}} \to 2\, \overset{+2}{N} \overset{-2}{O_{(g)}}$
It is a combination (combustion) type of redox reaction
(b) $2\,\overset{+2}{pb}\overset{+5-2}{(NO_{3})_{2(s)}} \to 2\,\overset{+2}{pb}\overset{-2}{O_{(s)}}+2\, \overset{+4}{N} \overset{-2}{O_{2(g)}}+\frac{1}{2}\overset{0}{O}_{2{(g)}}$
It is also a redox reaction involving decomposition of lead nitrate
(c) $\overset{+1}{Na}\overset{-1}{H_{(s)}}+\overset{+1}{H_{2}}\overset{-2}{O_{(l)}} \to \overset{+1}{Na}\overset{-2}{O}\overset{+1}{H_{(aq)}}+\overset{0}{H}_{2{(g)}}$
It is a displacement type of redox reaction in which hydrogen of water is displaced by a hydride ion into dihydrogen gas
(d) $2\, \overset{+4}{N}\overset{-2}{O_{2}}+2\, \overset{-2}{O}\overset{+1}{H} \to \overset{+3}{N}\overset{-2}{O^{-}_{2(aq)}}+\overset{+5}{N}\overset{-2}{O^{-}_{3(aq)}}+H_{2}O_{(l)}$
It is a disproportionation reaction in which the oxidation state of nitrogen changes from $+4$ to $+3$ and $+5$