Which half-reaction can occur at the anode in a
voltaic cell?
(1) ni2+ + > ni (3) zn--> zn2+ + 2e-
(2) sn + > sn2+ (4) fe3+--> fe2+ + e-

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.

a compound is a molecule made of atoms from different elements.

a. by the combination of an unlimited number of elements