For which of the following ionic species radius would be maximum?

Options

A. `C^(4-)`
B. `N^(3-)`
C. `O^(2-)`
D. `Mg^(2+)`

Explanation

To determine which ionic species has the maximum radius, we will analyze the given options based on their electron configurations and effective nuclear charge.

### Step-by-Step Solution:

1. **Identify the Ionic Species**: The options provided are C4-, N3-, O2-, and Mg2+.

2. **Determine the Number of Electrons**:
- **C4-**: Carbon (C) has an atomic number of 6, meaning it has 6 protons and, in its neutral state, 6 electrons. With a -4 charge, it gains 4 electrons, resulting in a total of 10 electrons.
- **N3-**: Nitrogen (N) has an atomic number of 7, so it has 7 protons and 7 electrons in its neutral state. With a -3 charge, it gains 3 electrons, resulting in a total of 10 electrons.
- **O2-**: Oxygen (O) has an atomic number of 8, so it has 8 protons and 8 electrons in its neutral state. With a -2 charge, it gains 2 electrons, resulting in a total of 10 electrons.
- **Mg2+**: Magnesium (Mg) has an atomic number of 12, so it has 12 protons and 12 electrons in its neutral state. With a +2 charge, it loses 2 electrons, resulting in a total of 10 electrons.

3. **Analyze the Effective Nuclear Charge**:
- **C4-**: 6 protons binding 10 electrons. The effective nuclear charge is low, leading to a larger radius.
- **N3-**: 7 protons binding 10 electrons. The effective nuclear charge is higher than C4-, resulting in a smaller radius than C4-.
- **O2-**: 8 protons binding 10 electrons. The effective nuclear charge is higher than N3-, resulting in a smaller radius than N3-.
- **Mg2+**: 12 protons binding 10 electrons. The effective nuclear charge is the highest, resulting in the smallest radius among the options.

4. **Compare the Ionic Radii**:
- Since all species have the same number of electrons (10), the one with the least number of protons will have the largest radius due to less effective nuclear charge.
- C4- has 6 protons, N3- has 7 protons, O2- has 8 protons, and Mg2+ has 12 protons.

5. **Conclusion**: The ionic species with the maximum radius is C4-.

### Final Answer:
The ionic species with the maximum radius is **C4-**.