Answer:
A. opposite spin of two electrons
Explanation:
Four quantum numbers identify electrons:
n - the principal number. It indicates the shell where the electron is, and it is from 1 to 7 and by the letters K, L, M, N, O, P, and Q.
l - the azimuthal number. It indicates the subshell where the electron is, and it varies from 0 to 3 and it is represented by the letters s, p, d, and f.
ml - the magnetic number. It represents the orbital where it is easy to find the electron. Each orbital supports two electrons, and it varies from -l to +l.
ms - the spin number. It represents the spin of the electron, which can be -1/2 or + 1/2. At the orbital, the electrons have different spins, which are represented by arrows, the up arrow represents the -1/2 and the down arrow the +1/2.
