How many boxcars are there in a long freight train if it takes the entire train 2.0 min to pass a station as it travels 40. Miles per hour? The box cars were 86 ft long

Acovalent bond is formed between the two hydrogen bonds

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.

Ithink carbon dioxide, i am not completely sure.tell me if i am wrong.