A statue coated with chemical substance X on long exposure to polluted atmosphere becomes black. This colour can be restored by treatment with `H_2O_2`. Identify element X and also the types of chemical changes involved.

Explanation

To solve the question step by step, we can follow this approach:

### Step 1: Identify the chemical substance X
The question states that a statue is coated with a chemical substance X, which becomes black upon exposure to a polluted atmosphere.

**Solution:**
The chemical substance X is lead oxide (PbO).

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