Correct Answer: John Dalton

Solution : The correct answer is John Dalton.

In the early 1800s, the English chemist John Dalton was credited with discovering and proposing the atomic theory. He suggested that each chemical element is made up of a unique type of atom and that atoms differ from one another based on their mass. Dalton suggested that each chemical element is made up of a unique type of atom, and all atoms of a given element are identical in their properties.