Which of the following is correct?

Options

A. lonicradius is proportional to atomic number.
B. lonic radius is inversely proportional to atomic mass.
C. Ionic radius is inversly proportional to effective nucelar charge.
D. All are correct.

Explanation

To solve the question regarding the correctness of the statements about ionic radius and its relationship with atomic number, atomic mass, and effective nuclear charge, we can analyze each statement step by step.

### Step-by-Step Solution:

1. **Understanding Ionic Radius and Atomic Number**:
- The first statement claims that ionic radius is proportional to atomic number.
- This statement is incorrect because, while ionic radius can increase down a group due to the addition of electron shells, it does not directly correlate with atomic number across periods.

**Hint**: Remember that ionic radius trends differ when moving down a group versus across a period.

2. **Understanding Ionic Radius and Atomic Mass**:
- The second statement asserts that ionic radius is proportional to atomic mass.
- This statement is also incorrect. Similar to atomic number, ionic radius does not have a direct proportional relationship with atomic mass across periods.

**Hint**: Consider how atomic mass is related to the number of protons and neutrons, but not directly to ionic size.

3. **Understanding Ionic Radius and Effective Nuclear Charge**:
- The third statement claims that ionic radius is inversely proportional to effective nuclear charge.
- This statement is correct. As the effective nuclear charge increases, the attraction between the nucleus and the electrons increases, leading to a decrease in ionic radius.

**Hint**: Think about how increased nuclear charge affects electron attraction and size.

4. **Conclusion**:
- The fourth statement claims that all previous statements are correct, which is false since we have identified that the first two statements are incorrect.
- Therefore, the only correct statement is the third one.

### Final Answer:
The correct statement is: **Ionic radius is inversely proportional to the effective nuclear charge.**