Answer:
The number of electrons in an orbit depends on the element. Hydrogen has 1, Helium has 2. Lithium has 2 in the inner orbit and 1 in the outer one.
Only a maximum of two electrons can occupy an orbital.
The orbital configuration of oxygen:
1s2 2s2 2px2 2py1 2pz1
The s orbital and the 2px orbitals have 2 electrons but the py and pz orbitals have 1 each.