Which is the first element to have 4d-electron in its electronic configurations

Options

A. Ac
B. Sc
C. Y
D. La

Answer

To determine which element is the first to have 4d electrons in its electronic configuration, we need to analyze the periodic table and the order of filling of electron orbitals.

### Step-by-Step Solution:

1. **Understanding Electron Configuration**:
- The electron configuration of an element describes the distribution of electrons among the various orbitals. The 4d orbital is filled after the 5s and 4p orbitals.

2. **Identifying the Elements**:
- The elements mentioned in the question are cadmium (Cd), yttrium (Y), lanthanum (La), and actinium (Ac).
- We need to find the first element that has electrons in the 4d subshell.

3. **Electron Configurations of the Elements**:
- **Cadmium (Cd)**: The electron configuration is [Kr] 4d10 5s2. This means that cadmium has filled the 4d subshell.
- **Yttrium (Y)**: The electron configuration is [Kr] 5s2 4d1. This indicates that yttrium has one electron in the 4d subshell.
- **Lanthanum (La)**: The electron configuration is [Xe] 6s2 5d1. This means lanthanum does not have 4d electrons.
- **Actinium (Ac)**: The electron configuration is [Rn] 7s2 6d1. This means actinium does not have 4d electrons either.

4. **Determining the First Element with 4d Electrons**:
- From the configurations, we see that yttrium (Y) is the first element that has an electron in the 4d subshell, as it has the configuration [Kr] 5s2 4d1.

5. **Conclusion**:
- Therefore, the first element to have 4d electrons in its electronic configuration is **yttrium (Y)**.

### Final Answer:
The first element to have 4d electrons in its electronic configuration is **yttrium (Y)**.