MDCAT Chemistry MCQ #872

Why does the 4s orbital fill before the 3d orbital in electron configuration?

MDCAT Chemistry MCQ #872

  1. Question 1

    Q1. Why does the 4s orbital fill before the 3d orbital in electron configuration?

    • A) 4s has higher energy than 3d
    • B) 4s is closer to the nucleus than 3d
    • C) 3d orbitals have more subshells
    • D) Penetration effect makes 4s lower energy

    Answer: Penetration effect makes 4s lower energy

    Explanation: Penetration reduces 4s energy below 3d. Option B is a distractor since proximity isn't the primary factor.