Which set does not show correct matching ?

Options

A. `Cr = [Ar] 3d^(5)4s^(1)`, element belongs to `6^(th)` group.
B. `Fe^(2+) =[Ar]3d^(6)`, element belongs to `8^(th)` group.
C. `Sc^(3+) = [Ne] 3s^(2)3p^(6)`, element belongs to zero/eighteen group.
D. All of the above

Explanation

To solve the question of which set does not show correct matching, we will analyze the electronic configurations and group placements of the elements mentioned: Chromium, Iron, and Scandium.

### Step-by-Step Solution:

1. **Identify the Atomic Number and Electronic Configuration of Chromium:**
- Atomic Number: 24
- Electronic Configuration: [Ar] 3d⁵ 4s¹
- Outermost Electrons: 5 (from 3d) + 1 (from 4s) = 6 electrons
- Group: 6th group (due to 6 outermost electrons)
- Conclusion: This is a correct matching.

2. **Identify the Atomic Number and Electronic Configuration of Iron:**
- Atomic Number: 26
- Electronic Configuration: [Ar] 3d⁶ 4s²
- When Iron loses 2 electrons (to form Fe²⁺), the configuration becomes: [Ar] 3d⁶ 4s⁰
- Outermost Electrons: 6 (from 3d) + 0 (from 4s) = 6 electrons
- Group: 8th group (due to 8 outermost electrons)
- Conclusion: This is a correct matching.

3. **Identify the Atomic Number and Electronic Configuration of Scandium:**
- Atomic Number: 21
- Electronic Configuration: [Ne] 3s² 3p⁶ 3d¹
- Outermost Electrons: 2 (from 3s) + 0 (from 3p) + 1 (from 3d) = 3 electrons
- Group: 3rd group (due to 3 outermost electrons)
- When Scandium loses 3 electrons (to form Sc³⁺), the configuration becomes: [Ne] 3s⁰ 3p⁶ 3d⁰
- Conclusion: The information stating that Scandium belongs to the 18th group is incorrect since it actually belongs to the 3rd group.

4. **Final Conclusion:**
- The incorrect matching is for Scandium, which is stated to belong to the 18th group instead of the 3rd group. Therefore, option C is the correct answer.