If the nitrogen atom had electronic configuration $1s^7$,it would have energy lower than that of the normal ground state configuration $1s^2, 2s^2, 2p^3$ because the electrons would be closer to the nucleus. Yet,$1s^7$ is not observed because it violates:

• A
  Heisenberg's uncertainty principle
• B
  Hund's rule
• C
  Pauli's exclusion principle
• D
  Bohr postulate of stationary orbit