UPSC Prelims 2003 Q98: Science & Technology – Physics
Regarding the atom of a chemical element, the magnetic quantum number refers to
- (a) orientation
- (b) shape
- (c) size
- (d) spin
Answer: (a) orientation
Explanation
Magnetic quantum number
| Quantum number | Describes |
|---|---|
| Principal (n) | Size and energy of the shell |
| Azimuthal (l) | Shape of the orbital |
| Magnetic (m) | Orientation of the orbital in space |
| Spin (s) | Spin of the electron |
The magnetic quantum number refers to the orientation of the orbital in space.
Answer: (a) orientation.
Why each option is right or wrong
- (a) CORRECT. The magnetic quantum number gives the orientation.
- (b) Incorrect. The azimuthal quantum number gives the shape.
- (c) Incorrect. The principal quantum number gives the size.
- (d) Incorrect. The spin quantum number gives the spin.
Key point
n size, l shape, m orientation, s spin.
Remember
The magnetic quantum number gives the orientation of the orbital.
Common mistakes
- Mixing the shape with the orientation of orbitals.
- Giving size as the meaning of the m number.
- Confusing m with the spin quantum number.
Exam tip
Mnemonic: n - size, l - shape, m - orientation, s - spin.
Sources
- NCERT Class XI Chemistry — Structure of Atom
- Peter Atkins and Julio de Paula — Atkins' Physical Chemistry (Atomic structure and spectra)