Concentrated `HNO_3` and concentrated `H_2SO_4` can t be used for the preparation of `H_2S`. Give reason

Explanation

To answer the question of why concentrated HNO3 (nitric acid) and concentrated H2SO4 (sulfuric acid) cannot be used for the preparation of H2S (hydrogen sulfide), we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Reactants**:
- Concentrated HNO3 and H2SO4 are both strong acids and strong oxidizing agents. This means they have the ability to oxidize other substances.

2. **Oxidizing Nature of the Acids**:
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