Assertion : Anions are larger in size than the parent atom. Reason : In an anion, the number of protons in the nucleus is less than the number of electrons moving around it.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion.
B. If both assertion and reason are true but reason is not the correct explanation of assertion.
C. If assertion is true but reason is false.
D. If both assertion and reason are false.

Explanation

### Step-by-Step Solution

1. **Understanding Anions and Parent Atoms**:
- An anion is formed when a neutral atom (parent atom) gains one or more electrons. This results in a negatively charged ion.
- For example, if a neutral chlorine atom (Cl) gains an electron, it becomes a chloride ion (Cl⁻).

2. **Comparing Sizes**:
- The size of an anion is larger than its parent atom. This is because when an atom gains electrons, the additional negative charge causes the electron cloud to expand.
- In a neutral atom, the number of protons (positive charges) is equal to the number of electrons (negative charges), resulting in a balanced pull on the electrons.

3. **Effect of Protons and Electrons**:
- In the case of an anion, the number of electrons exceeds the number of protons. For example, in a chloride ion (Cl⁻), there are 17 protons and 18 electrons.
- The increased number of electrons means that the positive charge from the protons is not sufficient to pull the electrons in tightly, leading to a larger atomic radius.

4. **Conclusion**:
- Therefore, the assertion that "Anions are larger in size than the parent atom" is true.
- The reason provided, "In an anion, the number of protons in the nucleus is less than the number of electrons moving around it," is also true and correctly explains why anions are larger.

5. **Final Answer**:
- Both the assertion and the reason are correct, and the reason correctly explains the assertion.