Electronic confriguration of a transition element X in +3 oxidation states is `[Ar]3d^(5)`.
What is its atomic number?

Options

A. 25
B. 26
C. 27
D. 24

Explanation

To find the atomic number of the transition element \( X \) with the given electronic configuration in the +3 oxidation state, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the given electronic configuration**: The electronic configuration of the element \( X \) in the +3 oxidation state is given as \([Ar] 3d^5\).

2. **Understand the oxidation state**: The +3 oxidation state indicates that the element has lost 3 electrons compared to its neutral state.

3. **Determine the configuration of the neutral atom**:
- The configuration \([Ar] 3d^5\) means that in the neutral state, the element would have 3 more electrons than in the +3 state.
- Therefore, the neutral configuration would be \([Ar] 3d^5 4s^2\) (since transition metals fill the 4s orbital before the 3d orbital).

4. **Calculate the total number of electrons in the neutral atom**:
- The atomic number of Argon (Ar) is 18.
- Adding the electrons from the 3d and 4s orbitals:
\[ \text{Total electrons} = 18 + 5 + 2 = 25 \]

5. **Determine the atomic number**:
- The atomic number of the neutral atom \( X \) is 25.

6. **Confirm the oxidation state**:
- If the neutral atom has 25 electrons, losing 3 electrons (to form the +3 oxidation state) would leave it with:
\[ 25 - 3 = 22 \text{ electrons} \]
- This matches the configuration \([Ar] 3d^5\) because it indicates that the remaining electrons correspond to the +3 state.

### Conclusion:
The atomic number of the transition element \( X \) is **25**.