How many quantum numbers are used to describe an electron?
Four quantum numbers: L, N, M, S.
L, is the principal quantum number, an integer from 1 to N that describes its energy level;
N, is the subsidiary quantum number, between 0 and N-1, describing the number and type of orbitals;
M, is the magnetic quantum number, describing the orientation of orbitals;
S, is the spin, either up or down.