Which subshell is filled after the filling of 4p subshell?

Answer

To determine which subshell is filled after the filling of the 4p subshell, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Order of Subshell Filling**:
The order of filling subshells is determined by the Aufbau principle, which states that electrons occupy the lowest energy orbitals first. The general order of filling is based on the (n + l) rule, where 'n' is the principal quantum number and 'l' is the azimuthal quantum number.

2. **Determine the Quantum Numbers for 4p**:
The 4p subshell has:
- Principal quantum number (n) = 4
- Azimuthal quantum number (l) = 1 (for p orbitals)

3. **Calculate (n + l) for 4p and Subsequent Subshells**:
- For 4p: n + l = 4 + 1 = 5
- For 5s: n + l = 5 + 0 = 5
- For 4d: n + l = 4 + 2 = 6

4. **Compare the (n + l) Values**:
Since both 4p and 5s have the same (n + l) value of 5, we need to compare their principal quantum numbers (n). The 5s subshell has a lower principal quantum number (n = 5) compared to the 4d subshell (n = 4). Therefore, the 5s subshell is filled before the 4d subshell.

5. **Conclusion**:
After the filling of the 4p subshell, the next subshell to be filled is the 5s subshell.

### Final Answer:
The subshell that is filled after the filling of the 4p subshell is the **5s subshell**.