Explanation:

- Atoms combine in the ratio of small whole numbers to form:

- Option 1: Neutrons: Neutrons are subatomic particles within an atom's nucleus. They do not form through chemical combination.

- Option 2: Molecules: Molecules are formed when two or more atoms bond together chemically. However, Dalton's theory specifically focuses on compounds.

- Option 3: Protons: Like neutrons, protons are subatomic particles found in the nucleus. Atoms don’t combine to form protons.

- Option 4: Compounds: Compounds are substances with atoms of two or more different elements combined in fixed ratios. ?? Correct Answer: Compounds are formed according to Dalton's atomic theory.