Magnetic Quantum number determines

Concept: Each of the four quantum numbers describes a different property of an electron's state in an atom — the principal quantum number (n) sets the shell size and dominant energy, the azimuthal (angular momentum) quantum number (l) sets the orbital's shape (s, p, d, f), the magnetic quantum number (ml) sets the orbital's spatial orientation relative to a reference axis, and the spin quantum number (ms) sets the electron's intrinsic spin direction.

Application: For a given l, ml takes integer values from -l to +l, and each value corresponds to a distinct spatial orientation of that orbital — for example, the three p orbitals (px, py, pz) share the same shape and the same energy but differ only in orientation, distinguished by ml. So the property fixed by the magnetic quantum number is the orientation of orbitals.

Cross-check — why the other properties belong to different quantum numbers:

• Shape of orbitals is fixed by the azimuthal (angular momentum) quantum number l, not by the magnetic quantum number.

• Total energy of an orbital is fixed chiefly by the principal quantum number n (and, in multi-electron atoms, jointly with l); ml does not affect it in the absence of an external field.

• Spin of an electron is fixed by the separate spin quantum number ms, independent of ml.

Result: the magnetic quantum number determines the orientation of orbitals in space.