Which of the following is/are correct order regarding radius ?

Options

A. `Be^(+2) lt B^(+3) lt Li^(+)`
B. `B^(+3) lt Be^(+2) lt Li^(+)`
C. `F^(-) lt O^(-2) lt N^(-3)`
D. `B^(+3) lt Ga^(+3) lt Al^(+3)`

Answer

To determine the correct order regarding the radius of the given cations and anions, we need to follow a systematic approach based on the principles of ionic radii and the periodic trends.

### Step-by-Step Solution:

1. **Understand Ionic Radii Trends**:
- For **cations**: As the charge on the cation increases, the ionic radius decreases. This is because a higher positive charge pulls the electrons closer to the nucleus, resulting in a smaller radius.
- For **anions**: As the charge on the anion increases, the ionic radius increases. This is due to the addition of electrons, which increases electron-electron repulsion and results in a larger radius.

2. **Analyze the Given Options**:
- Look at the provided options and identify the cations and anions listed.
- For cations, check the charge and apply the trend: higher charge = smaller radius.
- For anions, check the charge and apply the trend: higher charge = larger radius.

3. **Consider Electronic Configuration**:
- When comparing ions of the same element or group, consider their electronic configurations. The presence of d-electrons can affect the size due to the phenomenon of d-orbital contraction.
- For example, when comparing aluminum (Al³⁺) and gallium (Ga³⁺), gallium has d-electrons which cause a contraction in size compared to aluminum.

4. **Evaluate Each Option**:
- For each option, determine if the order presented aligns with the trends discussed.
- Identify any exceptions, such as the case with gallium being smaller than aluminum despite being lower in the group.

5. **Identify the Correct Order**:
- After evaluating all options based on the trends and exceptions, identify which option correctly represents the ionic radii.

### Conclusion:
After analyzing the options and applying the principles of ionic radii, the correct order regarding radius is found in option four, which correctly accounts for the trends and exceptions in ionic sizes.