Question

The orbital which is filled with electrons immediately after '3p' is -

• A. 4s
• B. 3d
• C. 4f
• D. 4p

Answer 1

The Correct Option is A

To solve this problem, we need to follow the order of electron filling based on the Aufbau principle, which tells us the sequence of orbital filling according to increasing energy levels.

1. Electron Configuration Order:
The order of orbital filling is:
1s → 2s → 2p → 3s → 3p → 4s → 3d → 4p → ...

2. After 3p:
According to the Aufbau principle, after electrons fill the 3p orbital, the next orbital to be filled is 4s — not 3d or 4p.

3. Evaluating the Options:
(A) 4s – Correct ✅
(B) 3d – Incorrect (filled after 4s)
(C) 4f – Incorrect (comes much later)
(D) 4p – Incorrect (comes after 3d)

Final Answer:
The correct option is (A) 4s.