Question Detail
Question
Which principle explains why electrons occupy the (3d) orbital only after the (4s) orbital is filled?
Correct Answer
Option B is the correct answer.
Detailed Explanation
The Aufbau principle states that electrons fill orbitals in order of increasing energy. The 4s orbital is lower in energy than 3d for neutral atoms, so it fills first.
Hint
Remember the order of filling: 1s, 2s, 2p, 3s, 3p, 4s, 3d...