After np orbitals are filled, the next orbital filled will be :-

Options

A. `(n+1) s`
B. `(n+2)p`
C. `(n+1) d`
D. `(n+2) s`

Explanation

To solve the question of which orbital is filled after the np orbitals, we can follow these steps:

### Step 1: Understand the Aufbau Principle
The Aufbau principle states that electrons fill orbitals starting from the lowest energy level to the highest. The order of filling is determined by the n + l rule, where n is the principal quantum number and l is the azimuthal quantum number.

### Step 2: Determine the n + l Values
For the np orbitals:
- The principal quantum number (n) is the same for all np orbitals.
- The azimuthal quantum number (l) for p orbitals is 1.
- Therefore, the n + l value for np orbitals is n + 1.

### Step 3: Identify the Next Orbital
After filling the np orbitals, we need to find the next orbital to be filled. According to the Aufbau principle, we compare the n + l values of the orbitals:
- For the ns orbital (where n is the principal quantum number for the next shell), the azimuthal quantum number (l) is 0.
- Therefore, the n + l value for ns orbitals is n + 0 = n.

### Step 4: Compare n + l Values
Now we compare the n + l values:
- np orbitals: n + 1
- ns orbitals: n

Since n + 1 (for np) is greater than n (for ns), the ns orbital will be filled next after the np orbitals.

### Conclusion
Thus, the next orbital to be filled after the np orbitals is the ns orbital.

### Final Answer
**The next orbital filled after np orbitals is the ns orbital.**