MDCAT Chemistry MCQ #859

Why is the 4s orbital filled before the 3d orbital according to electron configuration rules?

MDCAT Chemistry MCQ #859

  1. Question 1

    Q1. Why is the 4s orbital filled before the 3d orbital according to electron configuration rules?

    • A) 4s has lower energy than 3d
    • B) 3d orbitals are fully shielded
    • C) 4s is closer to the nucleus
    • D) 3d has higher angular momentum

    Answer: 4s has lower energy than 3d

    Explanation: Aufbau principle fills orbitals by energy: 4s is lower energy than 3d in ground states.