Q. 12 For a 4s orbital of hydrogen atom, the magnetic quantum number (ml) is
The magnetic quantum number (ml) for the 4s orbital of a hydrogen atom is 0, making option (D) correct.
Quantum Numbers Overview
Quantum numbers describe electron states in atoms. The principal quantum number (n=4 for 4s) indicates energy level and size. The azimuthal quantum number (l=0 for s orbitals) defines subshell shape, while ml specifies orbital orientation, ranging from -l to +l.
Correct Answer: Option (D) 0
For 4s orbital, n=4 and l=0 (s subshell). Thus, ml values are only 0, as -0 to +0 yields a single orientation. S orbitals are spherical with one ml value.
Why Other Options Wrong
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(A) 4: ml cannot equal n; maximum ml is l, which is 0 here.
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(B) 3: Requires l=3 (f orbital), not applicable to s.
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(C) 1: Suits p orbitals (l=1), where ml=-1,0,+1 possible.
| Option | ml Value | Reason Incorrect for 4s |
|---|---|---|
| A | 4 | Exceeds l=0 limit |
| B | 3 | Matches f subshell (l=3) |
| C | 1 | Matches p subshell (l=1) |
| D | 0 | Correct for s (l=0) |
Key Concepts for Exams
S orbitals (l=0) always have ml=0, holding up to 2 electrons with opposite spins. This MCQ tests subshell identification in hydrogen atomic orbitals.
