Answer:
After the 4s sublevel is filled with two electrons, ten electrons fill the 3d sublevel, which is slightly higher in energy than the 4s sublevel. After the 3d sublevel is filled, the remaining three electrons will be in orbitals in the 4p sublevel. Thus, the electron configuration for arsenic is [Ar] 4s(2 squared) 3d(10 squared) 4p(3 squared).
