`Pb(NO_(3))_(2)` on heating gives a brown gas which undergoes dimerization on cooling? Identify the gas.

Explanation

To solve the problem, we need to identify the gas produced when lead nitrate, \( \text{Pb(NO}_3\text{)}_2 \), is heated and which undergoes dimerization upon cooling.

### Step-by-Step Solution:

1. **Understanding the Reaction**:
Lead nitrate decomposes upon heating. The general decomposition reaction for lead nitrate is:
\[
\text{2 Pb(NO}_3\text{)}_2 \rightarrow \text{2 PbO} + \text{4 NO}_2 + \text{O}_2
...