What does synthesis gas (water gas) consist of?

a. oxygen (O2) and hydrogen (H2)
b. methane (CH4) and water (H2O)
c. carbon dioxide (CO2) and hydrogen (H2)
d. carbon monoxide (CO) and hydrogen (H2)

7is b8 is d9 is c10 is a11 is d

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.