Which of the following molecules are homoatomic ?
(i) `H_(2)O`, (ii) `O_(3)`, (iii) `NH_(3)`, (iv) `Cl_(2)`

Answer

To determine which of the given molecules are homoatomic, we need to understand the definition of a homoatomic molecule. A homoatomic molecule is one that consists of atoms of the same element.

Let's analyze each option:

1. **H₂O (Water)**:
- Composition: 2 Hydrogen (H) atoms and 1 Oxygen (O) atom.
- Since it contains atoms of different elements (H and O), H₂O is **not** a homoatomic molecule.

2. **O₃ (Ozone)**:
- Composition: 3 Oxygen (O) atoms.
- All atoms are of the same element (Oxygen), so O₃ is a homoatomic molecule.

3. **NH₃ (Ammonia)**:
- Composition: 1 Nitrogen (N) atom and 3 Hydrogen (H) atoms.
- Since it contains atoms of different elements (N and H), NH₃ is **not** a homoatomic molecule.

4. **Cl₂ (Chlorine gas)**:
- Composition: 2 Chlorine (Cl) atoms.
- All atoms are of the same element (Chlorine), so Cl₂ is a homoatomic molecule.

Based on this analysis, the homoatomic molecules from the options provided are:

- **O₃** (Ozone)
- **Cl₂** (Chlorine gas)

Thus, the answer to the question is that the homoatomic molecules are **O₃ and Cl₂**.

### Summary of the Solution:
- H₂O: Not homoatomic (different elements).
- O₃: Homoatomic (same element).
- NH₃: Not homoatomic (different elements).
- Cl₂: Homoatomic (same element).