A 4 L sample of gas at 298 K and 2 atm contains 0.250 mol of gas. If we add another 0.250 mol of gas at the same pressure and temperature, what is the final total volume of gas?

The problem here is that according to aufbau principle before 3d orbital 4s subshell comes.after filling 3p orbital with electrons you have 4 electrons left, you place two in 4s with opposite spin and the other two in 3d in any of its two orbitals of total five orbitals with the same spin.

Answer is (d)a brainliest would be appreciated