Electronic configuration of a transition element X in + 3 oxidation state 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 electronic configuration `[Ar] 3d^5` in the +3 oxidation state, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Given Configuration**: The electronic configuration provided is `[Ar] 3d^5`, which represents the configuration of the element in its +3 oxidation state.

2. **Identify the Oxidation State**: In the +3 oxidation state, the element has lost 3 electrons. This means that the original electronic configuration must have had 3 more electrons than what is shown in the +3 state.

3. **Determine the Original Configuration**:
- The given configuration in the +3 state is `[Ar] 3d^5`.
- To find the original configuration, we need to add back the 3 electrons that were lost during oxidation. The electrons are typically removed from the outermost shell first, which includes the 4s and then the 3d subshell.
- Therefore, the original configuration before losing 3 electrons would be `[Ar] 3d^6 4s^2`.

4. **Count the Electrons**:
- The atomic number corresponds to the total number of electrons in a neutral atom.
- The configuration `[Ar]` corresponds to 18 electrons (the atomic number of Argon).
- The `3d^6` indicates 6 electrons in the 3d subshell.
- The `4s^2` indicates 2 electrons in the 4s subshell.
- Adding these together gives:
\[ \text{Total electrons} = 18 + 6 + 2 = 26 \]

5. **Conclusion**: The atomic number of the element X is 26.

### Final Answer:
The atomic number of the transition element X is **26**.