Question

Which of the following orbit has lowest energy?

• A. $2p$
• B. $3s$
• C. $3d$
• D. $4s$
• E. $3p$

Answer 1

The correct option is A $2p$

The order of filling electrons, as per $"n+l"$ rule is as follows:
$1s,2s,2p,3s,3p,4s,3d,4p,5s,4d,5p,6s,4f,5d,6p,7s,5f,6d,7p$
This order corresponds to the increasing order of energies.
Hence, the lowest energy is for the $2p.$