When electrons pair in orbitals around an atom whats the best description of why it happens, theres a bit of variation of the answers on google. The lowest energy state is the most favourable, therefore electrons will inhabit the orbitals of the lowest energy first ie. 1s, 2s, 2d and so on. However due to the Pauli exclusion principle no 2 fermions can occupy the same quantum state, however electrons with opposite spin numbers do not have the same quantum state therefore 2 electrons of opposite spins can occupy the same orbital. It just the explaination in my chemistry books starts talking about repulsion and stuff but the above sounds more concise?