(A) 1s < 2p < 3d < 4s

(B) 1s < 2s = 2p < 3s = 3p

(C) 1s < 2s < 2p < 3s < 3p

(D) 1s < 2s < 4s < 3d

Choose the correct answer from the options given below:

In hydrogen atom, energy depends only on principal quantum number (n), not on l value.

Energy order:
1s < (2s = 2p) < (3s = 3p = 3d) < (4s = 4p = 4d = 4f)

1s < 2p < 3d < 4s ✔
Correct energy order → Correct

1s < 2s = 2p < 3s = 3p ✔
Matches hydrogen energy rule → Correct

2s < 2p ❌ (same energy in H atom)
Hence sequence is wrong → Incorrect

4s < 3d ❌ (n = 4 orbitals have higher energy than n = 3)
Hence sequence is wrong → Incorrect

Correct Answer = (C) and (D) only