When `3d` orbital is complete, the new electron will enter the

Options

A. 4 p-orbital
B. 4 f-orbital
C. 4 s-orbital
D. 4 d-orbital

Explanation

To answer the question "When the 3d orbital is complete, the new electron will enter the:", we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Orbital Filling Order**:
- Electrons fill atomic orbitals in a specific order based on their energy levels. The order is determined by the Aufbau principle, which states that electrons occupy the lowest energy orbitals first.

2. **Identify the 3d Orbital**:
- The 3d orbital is part of the third energy level (n=3). It can hold a maximum of 10 electrons.

3. **Determine the Next Orbital**:
- After the 3d orbital is filled, we need to find out which orbital has the next lowest energy level for the next electron to enter.

4. **Calculate N + L Values**:
- For the 3d orbital:
- n = 3 (principal quantum number)
- l = 2 (for d orbitals)
- N + L = 3 + 2 = 5
- For the 4s orbital:
- n = 4
- l = 0 (for s orbitals)
- N + L = 4 + 0 = 4
- For the 4p orbital:
- n = 4
- l = 1 (for p orbitals)
- N + L = 4 + 1 = 5
- For the 4d orbital:
- n = 4
- l = 2 (for d orbitals)
- N + L = 4 + 2 = 6

5. **Compare N + L Values**:
- The 4s orbital has the lowest N + L value (4), which means it has lower energy than both the 3d and 4p orbitals.
- The 3d orbital has an N + L value of 5, and the 4p orbital also has an N + L value of 5, but since the principal quantum number (n) for 4p is higher (n=4) than that of 3d (n=3), 3d is filled before 4p.

6. **Conclusion**:
- Therefore, when the 3d orbital is complete, the next electron will enter the 4s orbital before it goes to the 4p orbital.

### Final Answer:
When the 3d orbital is complete, the new electron will enter the **4s orbital**.