In the main group elements
(i) as we proceed down the same group in the periodic table and
(ii) as we proceed from left to right in the same period, the atomic radius

Options

A. (i) Increase continuously, (ii) Decreases continuously
B. (i) Decreases continuously, (ii) Increases continuously
C. (i) Increases continuously, (ii) Decreases upto the group IV and then increases upto the end of the period
D. (i) Decreases continuously, (ii) Decreases upto the group IV and then increases upto the end of the period

Answer

### Step-by-Step Solution:

1. **Understanding Atomic Radius**: The atomic radius is defined as the distance from the nucleus of an atom to the outermost shell of electrons. It can vary based on the position of the element in the periodic table.

2. **Effect of Moving Down a Group**:
- As we move down a group in the periodic table (from top to bottom), the atomic radius **increases**.
- **Reason**: This increase occurs because:
- The atomic number increases, meaning there are more protons in the nucleus.
- More electron shells are added as we move down, which means the outermost electrons are further away from the nucleus.
- The increased distance outweighs any increase in nuclear charge, leading to a larger atomic radius.

3. **Effect of Moving Across a Period**:
- As we move from left to right across a period, the atomic radius **decreases**.
- **Reason**: This decrease occurs because:
- The atomic number increases, which means more protons are present in the nucleus.
- The increase in positive charge in the nucleus pulls the electrons closer to the nucleus due to increased electrostatic attraction.
- As a result, the outermost electrons are drawn closer, leading to a smaller atomic radius.

4. **Conclusion**:
- In summary, as we proceed down a group, the atomic radius increases, and as we proceed from left to right in a period, the atomic radius decreases.

### Final Answer:
- (i) Down a group: Atomic radius **increases**.
- (ii) Across a period: Atomic radius **decreases**.

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