Ionic radii are

Options

A. inversely proportional to effective nuclear charge
B. inversely proportional to square of effective nuclear charge
C. directly proptional to effective nuclear charge
D. directly proportional to sqaure of effect nuclear charge

Explanation

To solve the question regarding the relationship between ionic radii and effective nuclear charge, we can break it down into a series of steps:

### Step-by-Step Solution:

1. **Understand the Concept of Effective Nuclear Charge (Z_eff)**:
- Effective nuclear charge is the net positive charge experienced by an electron in a multi-electron atom. It takes into account the actual nuclear charge (Z) and the shielding effect caused by inner-shell electrons.

2. **Define Ionic Radii**:
- Ionic radii refer to the size of an ion. Cations (positively charged ions) are generally smaller than their parent atoms due to the loss of electrons and increased effective nuclear charge on the remaining electrons. Anions (negatively charged ions) are larger than their parent atoms due to the addition of electrons and increased electron-electron repulsion.

3. **Analyze the Relationship**:
- As the effective nuclear charge increases, the attraction between the nucleus and the electrons also increases. This leads to a decrease in the size of the ion (or atomic radius).
- Therefore, we can conclude that the ionic radius is inversely proportional to the effective nuclear charge.

4. **Evaluate the Options**:
- The options provided are:
- A) Inversely proportional to effective nuclear charge
- B) Inversely proportional to square of effective nuclear charge
- C) Directly proportional to effective nuclear charge
- D) Directly proportional to square of effective nuclear charge
- Based on our analysis, the correct answer is **A) Inversely proportional to effective nuclear charge**.

5. **Final Conclusion**:
- The ionic radii decrease as the effective nuclear charge increases, confirming that they are inversely related.