Atoms that differ only in the number of neutrons are called: (a) protons (b) atomic mass unit (c) isotopes (d) compounds

if two electrons have the same n, the same ℓ, and the same ml, then they are in the same orbital. the pauli exclusion principle states that no two identical fermions (a fancy word for electrons and other subatomic particles like electrons) may occupy the same quantum state in an atom simultaneously.