what represents the proper order to fill electron orbitals from 1s to 4p.

Answer 1

1s2s2p3s3p4s3d

According to Aufbau principle, electron fill in the lowest energy levels and sub-shells first. In terms of energy

1s<2s<2p<3s<3p<4s<3d<4p<5s<4d

Notice 4s is filled before 3d, 4s lower energy than 3d. There are some exceptions in the d-block of the periodic table around Cr.