When `PbO_2` reacts with conc `HNO_3`,

Explanation

To solve the question of what happens when PbO2 reacts with concentrated HNO3, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Reactants**: The reactants in this reaction are lead dioxide (PbO2) and concentrated nitric acid (HNO3).

2. **Write the Chemical Equation**: The reaction can be represented by the following chemical equation:
\[ \text{PbO}_2 + 4 \text{HNO}_3 \rightarrow \text{Pb(NO}_3\text{)}_2 + 2 \text{H}_2\text{O} + \text{O}_2 \]

3. **Identify the Products**: The products of this reaction are lead(II) nitrate (Pb(NO3)2), water (H2O), and oxygen gas (O2).

4. **Determine the Gas Evolved**: From the balanced equation, we can see that the gas evolved during this reaction is oxygen (O2).

5. **Identify the Role of PbO2**: In this reaction, lead dioxide (PbO2) acts as an oxidizing agent.

### Final Answer:
When PbO2 reacts with concentrated HNO3, the reaction produces lead(II) nitrate (Pb(NO3)2), water (H2O), and oxygen gas (O2). The gas evolved is oxygen, and PbO2 acts as an oxidizing agent.

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