Each molecule of hydrochloric acid, hcl, contains one atom of hydrogen and
a. one atom of chlorine.
c. two atoms of chlorine.
b. one atom of oxygen.
d. two atoms of oxygen.

A.) Each molecule of hydrochloric acid, HCl, contains one atom of hydrogen and "One atom of Chlorine"

Hope this helps!

If you explain it more through i will answer it : )

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.