Generated by claude-sonnet-4-6 · 2026-06-14 10:28 · grounding rag
Model Answer
(a)
The correct answer is (a): thermal decomposition of lead nitrate which produces brown fumes of nitrogen dioxide.
Reaction: $2\text{Pb(NO}_3)_2(s) \xrightarrow{\Delta} 2\text{PbO}(s) + 4\text{NO}_2(g) + \text{O}_2(g)$
The brown fumes are of NO₂ gas, produced by thermal decomposition (not oxidation) of lead nitrate.
Source: Chapter 1, Activity 1.6 — Decomposition Reaction
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Explanation
- The key distinction: the reaction is thermal decomposition (a single reactant breaks down on heating), not oxidation.
- The brown fumes are specifically nitrogen dioxide (NO₂), not lead oxide (PbO is a solid yellow powder, not a fume).
- Option (b) is wrong because PbO is a solid, not a fume.
- Options (c) and (d) are wrong because the reaction type is decomposition, not oxidation.
- Remember the balanced equation — it also produces O₂, but the visible brown fumes are NO₂ only.