Question

According to the Aufbau’s principle, which of the following orbital should be filled first?

(a) 5d

(b) 4p

(c) 3p

(d) 2s

The question was posed to me at a job interview.

I would like to ask this question from Quantum Mechanical Model of Atom topic in section Structure of Atom of Chemistry – Class 11

Answer 1

The correct choice is (d) 2s

Best explanation: As per the Aufbau’s principle, the orbital or subshell with the lowest energy should be filled first. The ascending order of orbital’s energy is given by 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 4f, 5d, 6p, 7s. So 2s orbital should be filled first.