A ground state electron configuration, according to atomic science, follows the Aufbau principle in which all orbitals are filled in increasing energy. In this case, we just try to look up if the lower energy levels such as s-orbital are filled with 2 electrons, p has 6 electrons, d has 10, etc and follows the order of electronic configuration. Answer is C. 1s22s22p63s23p64s24d10
