Answer:
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.
