According to Slater's rule, correct order of `Z_(eff)` on valence shell electron is:

Options

A. `Fe gt Fe^(2+) gt Fe^(3+)`
B. `N^(3-) lt O^(2-) lt F^(-)`
C. `Na^(+) lt Mg^(2+) lt Al^(3+)`
D. `Tl^(2+) lt V^(3+) lt Mn^(5+)`

Explanation

To determine the correct order of effective nuclear charge (Z_eff) on valence shell electrons according to Slater's rule, we need to understand how Z_eff is calculated and the factors that influence it.

### Step-by-Step Solution:

1. **Understand Z_eff**:
- Z_eff (effective nuclear charge) is the net positive charge experienced by an electron in a multi-electron atom. It accounts for the actual nuclear charge (Z) and the shielding effect of other electrons.

2. **Apply Slater's Rule**:
- Slater's rule provides a method to estimate Z_eff. According to this rule, electrons in the same group shield each other less effectively than electrons in inner shells. The formula for Z_eff can be summarized as:
\[ Z_{\text{eff}} = Z - S \]
where S is the shielding constant.

3. **Identify the Elements**:
- For this problem, we will consider several ions: Na\(^+\), Mg\(^{2+}\), Al\(^{3+}\), Fe\(^{2+}\), and Fe\(^{3+}\).

4. **Calculate Z_eff for Each Ion**:
- **Na\(^+\)**: Z = 11 (11 protons), S = 2 (1s electrons shield 2 electrons). Thus, Z_eff = 11 - 2 = 9.
- **Mg\(^{2+}\)**: Z = 12, S = 2. Thus, Z_eff = 12 - 2 = 10.
- **Al\(^{3+}\)**: Z = 13, S = 2. Thus, Z_eff = 13 - 2 = 11.
- **Fe\(^{2+}\)**: Z = 26, S = 18 (considering 1s, 2s, 2p, 3s, 3p electrons). Thus, Z_eff = 26 - 18 = 8.
- **Fe\(^{3+}\)**: Z = 26, S = 18. Thus, Z_eff = 26 - 18 = 8.

5. **Compare Z_eff Values**:
- Now, we can compare the calculated Z_eff values:
- Na\(^+\): 9
- Mg\(^{2+}\): 10
- Al\(^{3+}\): 11
- Fe\(^{2+}\): 8
- Fe\(^{3+}\): 8

6. **Determine the Correct Order**:
- The order of Z_eff from highest to lowest is:
- Al\(^{3+}\) > Mg\(^{2+}\) > Na\(^+\) > Fe\(^{2+}\) = Fe\(^{3+}\)

### Final Answer:
The correct order of Z_eff on valence shell electrons according to Slater's rule is:
**Al\(^{3+}\) > Mg\(^{2+}\) > Na\(^+\) > Fe\(^{2+}\) = Fe\(^{3+}\)**.