what did dalton discover about the atoms that combine to form compounds?

a) they form whole-number ratios in the compound.

b) they physically mix together.

c) they change from one element to another.

d) they break into smaller pieces.

I believe it’s A, they form whole-number ratios in the compound

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.