Q. If n = 6, the correct sequence of filling of electrons will be
A) ns → np → (n−1)d → (n−2)f
B) ns → (n−2)f → (n−1)d → np
C) ns → (n−1)d → (n−2)f → np
D) ns → (n−2)f → np → (n−1)d
Explanation
[Solution from source] For n = 6 the Aufbau order is 6s → 4f → 5d → 6p (as in Cs, Ba, La/Ce onwards, Hf, then Tl), i.e. ns → (n−2)f → (n−1)d → np. Filling np before the inner d and f orbitals is the trap. Answer (2).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.