Assertion: 1 mol of O and 1 mol of `O_(2)` contain equal number of particles.
Reason: 1 mol of molecules is always double than 1 mol of atoms in all diatomic molecules.

Options

A. Assertion and reason both are correct statements and reason is correct explanation for assertion.
B. Assertion and reason both are correct statements but reason is not correct explanation for assertion.
C. Assertion is correct statements but reason is wrong statement.
D. Assertion is wrong statement but reason is correct statement.

Answer

To solve the question, we need to analyze both the assertion and the reason provided.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that "1 mol of O and 1 mol of O₂ contain equal number of particles."
- 1 mole of any substance contains Avogadro's number of entities, which is approximately \(6.022 \times 10^{23}\).
- Therefore, 1 mole of O (oxygen atoms) contains \(6.022 \times 10^{23}\) atoms.
- 1 mole of O₂ (oxygen molecules) contains \(6.022 \times 10^{23}\) molecules.
- Since the term "particles" can refer to both atoms and molecules, we can conclude that both 1 mole of O and 1 mole of O₂ contain \(6.022 \times 10^{23}\) particles each.

2. **Understanding the Reason**:
- The reason states that "1 mol of molecules is always double than 1 mol of atoms in all diatomic molecules."
- For a diatomic molecule like O₂, 1 mole of O₂ contains \(6.022 \times 10^{23}\) molecules.
- Each molecule of O₂ consists of 2 atoms of oxygen.
- Therefore, 1 mole of O₂ contains \(2 \times 6.022 \times 10^{23}\) atoms of oxygen.
- This means that the number of atoms in 1 mole of O₂ is indeed double the number of molecules in 1 mole of O₂, confirming the reason.

3. **Conclusion**:
- The assertion is true because both 1 mole of O and 1 mole of O₂ contain the same number of particles (Avogadro's number).
- The reason is also true because it correctly states the relationship between moles of diatomic molecules and the number of atoms they contain.
- Therefore, both the assertion and the reason are true.

### Final Answer:
- The assertion is true, and the reason is true, and the reason correctly explains the assertion.