] The gold foil is: • 4.00 x 10-7 metres thick
• 2400 atoms thick.
What is the diameter of one gold atom in metres?
Give your answer to 3 significant figures.​

U whay do you need with?

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.