After 3d-sub level is completely filled the differentiating electron enters into ….. sub level.

Options

A. 4s
B. 4p
C. 4f
D. 5s

Answer

To solve the question "After 3d-sub level is completely filled, the differentiating electron enters into which sub level?", we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Electron Configuration**:
- The electron configuration of an atom describes the distribution of electrons in atomic orbitals. Electrons fill orbitals in a specific order based on their energy levels.

2. **Identify the Order of Filling**:
- The order of filling of orbitals is determined by the Aufbau principle, which states that electrons occupy the lowest energy orbitals first. The general order of filling is:
- 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, etc.

3. **Locate the 3d Sublevel**:
- The 3d sublevel can hold a maximum of 10 electrons. Once this sublevel is completely filled (i.e., it has 10 electrons), we need to determine which sublevel is next in line for electron filling.

4. **Determine the Next Sublevel**:
- After the 3d sublevel, the next sublevel in the order of filling is the 4s sublevel. Therefore, after the 3d sublevel is completely filled, the next differentiating electron will enter the 4s sublevel.

5. **Conclusion**:
- Thus, the answer to the question is that after the 3d sublevel is completely filled, the differentiating electron enters into the 4s sublevel.

### Final Answer:
After the 3d sublevel is completely filled, the differentiating electron enters into the **4s sublevel**.

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