JEE Main · 2025 · 28 Jan 2025 · Shift 2 · Atomic Structure

In the hydrogen atom, with a single electron, orbital energy depends only on the principal quantum number $n$, not on $l$; orbitals sharing the same $n$ are degenerate, and a larger $n$ always sits higher regardless of subshell.

(A) $1s<2p<3d<4s$: each step moves to a strictly higher $n$ (1, 2, 3, 4) — correct.

(B) $1s<2s=2p<3s=3p$: correctly shows same-$n$ degeneracy — correct.

(C) $1s<2s<2p<3s<3p$: wrongly separates $2s$ and $2p$, which must be equal — not correct.

(D) $1s<2s<4s<3d$: places $4s$ below $3d$, but $n=4$ must sit above $n=3$ for hydrogen — not correct.

Statements (C) and (D) are the ones that are not correct.