According to `(n+l`) rule after completing 'np' level the electron enters int

Options

A. `(n-1)d`
B. `(n+1)s`
C. `nd`
D. `(n+1)p`

Explanation

To solve the question "According to (n+l) rule after completing 'np' level the electron enters into," we will follow a systematic approach based on the principles of electron configuration and the (n+l) rule.

### Step-by-Step Solution:

1. **Understanding the (n+l) Rule**:
- The (n+l) rule is used to determine the order in which electrons fill atomic orbitals. Here, 'n' is the principal quantum number and 'l' is the azimuthal quantum number.
- The rule states that electrons fill orbitals in order of increasing (n+l) values. If two orbitals have the same (n+l) value, the one with the lower 'n' value fills first.

2. **Identifying the Electron Configuration**:
- The electron configuration follows a specific order: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p, etc.
- After filling the 'np' level, we need to determine what comes next.

3. **Filling Order After 'np' Level**:
- After the 'np' level is filled, the next orbital to be filled is typically the (n+1)s orbital.
- For example, if we have filled 3p (where n=3), the next orbital to be filled is 4s (where n=4, which is 3+1).

4. **Generalizing the Filling Order**:
- After completing the np level, the electron will enter the (n+1)s orbital.
- This is because, according to the (n+l) rule, the (n+1)s orbital has a lower energy than the (n)d or (n)p orbitals of the next principal quantum number.

5. **Conclusion**:
- Therefore, after completing the 'np' level, the electron enters into the (n+1)s orbital.

### Final Answer:
According to the (n+l) rule, after completing the 'np' level, the electron enters into the **(n+1)s** orbital.

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