The order of filling orbitals is...
A1s, 2s, 2p, 3s, 3p, 3d, 4s, 4p
B1s, 2s, 2p, 3s, 3p, 3d, 4p, 3d
C1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p
D4p, 4s, 3d, 3p, 3s, 2p, 2s, 1s
A1s, 2s, 2p, 3s, 3p, 3d, 4s, 4p
B1s, 2s, 2p, 3s, 3p, 3d, 4p, 3d
C1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p
D4p, 4s, 3d, 3p, 3s, 2p, 2s, 1s