Mark the compound which is acid?

Options

A. `H_2 S`
B. `H_2 O`
C. `NH_3`
D. `NaOH`

Explanation

To determine which compound among H2S, H2O, Ammonia, and NaO is an acid, we can analyze each compound based on its ability to donate protons (H⁺ ions).

### Step-by-Step Solution:

1. **Identify the Compounds**: The compounds given are:
- H2S (Hydrogen Sulfide)
- H2O (Water)
- Ammonia (NH3)
- NaO (Sodium Oxide)

2. **Analyze H2S**:
- H2S is known as hydrogen sulfide. It can donate protons (H⁺ ions) and is classified as a weak acid.
- It has two hydrogen atoms, which means it can theoretically donate two protons, making it a diprotic acid.

3. **Analyze H2O**:
- Water (H2O) can act as both an acid and a base (amphoteric), but it is not classified as a strong acid. It can donate H⁺ ions but does so very weakly.

4. **Analyze Ammonia (NH3)**:
- Ammonia is a weak base and does not donate protons. Instead, it accepts protons to form NH4⁺ (ammonium ion). Therefore, it is not an acid.

5. **Analyze NaO (Sodium Oxide)**:
- Sodium oxide (NaO) is a basic oxide and does not donate protons. It reacts with acids but is not classified as an acid itself.

6. **Conclusion**:
- Among the compounds listed, H2S is the only one that can be classified as an acid due to its ability to donate protons.

### Final Answer:
**H2S (Hydrogen Sulfide) is the acid among the given compounds.**

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