List these electron subshells in order of increasing energy. 6p, 7s, 6s, 4f note for advanced students: you may assume these subshells are all in an atom with many electrons, not a hydrogen atom.

6s < 4f < 6p < 7s

Explanation:

The difference in energy of two subshells is decided by comparing their n+l value.

where;

n = Principle Quantum Number (main Shell)

l = Azimuthal Quantum Number

The greater the n+l value the greater is the energy of subshell. Also, if two subshells have same n+l value, the the subshell with lower n value will be having lesser energy.

So,

For,

6p = 6 + 1 = 7

7s = 7 + 0 = 7

6s = 6 + 0 = 6

4f = 4 + 3 = 7

Hence, 6s has the lowest energy, among 6p, 7s and 4f (all having same n+l values) 4f has lowest energy compared to 6p and 7s as it has lowest n value. And 6p has less energy than 7s.