Question: 53: Which of the following reactions is a decomposition redox reaction?
(1) 2 \mathrm{~Pb}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{~s}) \rightarrow 2 \mathrm{PbO}(\mathrm{s})+4 \mathrm{NO}_{2}(\mathrm{~g})+\mathrm{O}_{2}(\mathrm{~g})
(2) \mathrm{N}_{2}(\mathrm{~g})+\mathrm{O}_{2}(\mathrm{~g}) \rightarrow 2 \mathrm{NO}(\mathrm{g})
(3) \mathrm{Cl}_{2}(\mathrm{~g})+2 \mathrm{OH}^{-}(\mathrm{aq}) \rightarrow \mathrm{ClO}^{-}(\mathrm{aq})+\mathrm{Cl}^{-}(\mathrm{aq})+4 \mathrm{H}_{2} \mathrm{O}(\ell)
(4) \mathrm{P}_{4}(\mathrm{~s})+3 \mathrm{OH}^{-}(\mathrm{aq})+3 \mathrm{H}_{2} \mathrm{O}(\ell) \rightarrow \mathrm{PH}_{3}(\mathrm{~g})+3 \mathrm{H}_{2} \mathrm{PO}_{2}^{-}(\mathrm{aq})
Answer: Option (1)
Explanation:
A decomposition reaction is one in which a single compound breaks down into two or more simpler substances.
A redox reaction involves simultaneous oxidation and reduction.
In option (1), lead nitrate decomposes on heating into lead oxide, nitrogen dioxide, and oxygen.
\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2} \rightarrow \mathrm{PbO}+\mathrm{NO}_{2}+\mathrm{O}_{2}Oxidation states change during the reaction. Nitrogen changes from +5 in nitrate to +4 in \mathrm{NO}_{2}, showing reduction.
Oxygen changes from -2 in nitrate to 0 in \mathrm{O}_{2}, showing oxidation.
Thus, option (1) is both a decomposition reaction and a redox reaction.
Option (2) is a combination reaction.
Option (3) is a disproportionation reaction.
Option (4) is also a disproportionation reaction.
Therefore, the correct answer is option (1).