Which of the following is correct?

Options

A. `r_("ionic") prop Z`
B. `r_("ionic") prop Z_(eff)`
C. `r_("ionic") prop (1)/(Z_(eff))`
D. `r_("ionic") prop Z_(eff)^2`

Explanation

To solve the question regarding the correct statement about ionic radius and effective nuclear charge (Z-effective), we can break it down into a step-by-step analysis:

### Step-by-Step Solution:

1. **Understanding Ionic Radius**:
- Ionic radius refers to the size of an ion in a crystal lattice. It is an important factor in determining the properties of ionic compounds.

2. **Relationship Between Ionic Radius and Size**:
- The ionic radius is directly proportional to the size of the ion. This means that larger ions will have a larger ionic radius.

3. **Understanding Effective Nuclear Charge (Z-effective)**:
- The effective nuclear charge is the net positive charge experienced by an electron in a multi-electron atom. It accounts for the shielding effect of inner electrons.

4. **Relationship Between Ionic Radius and Z-effective**:
- The size of an ion is inversely proportional to the effective nuclear charge. This means that as the effective nuclear charge increases, the ionic radius decreases. This is because a higher Z-effective means that the nucleus has a stronger pull on the electrons, drawing them closer and reducing the size of the ion.

5. **Conclusion**:
- Based on the relationships discussed, we can conclude that the correct statement is that the ionic radius is inversely proportional to the effective nuclear charge (Z-effective). Thus, if Z-effective increases, the ionic radius decreases.

### Final Answer:
The correct statement is: "Ionic radius is inversely proportional to Z-effective."