In the early 1800s, who discovered that each chemical element is made up of a unique type of atom and that atoms differ by their mass?

Correct option is B

The correct answer is (b) John Dalton.
 John Dalton, an English chemist, physicist, and meteorologist, made significant contributions to the atomic theory in the early 1800s.
 Dalton proposed that each chemical element is composed of a unique type of atom and that these atoms differ by their mass.
 His work laid the foundation for modern atomic theory, emphasizing that atoms are the indivisible building blocks of matter.
 Dalton's atomic theory included the idea that atoms of the same element are identical in mass and properties, while atoms of different elements have different masses and properties.
 He also introduced the concept that chemical reactions involve the rearrangement of atoms, which combine in fixed ratios to form compounds.
 Dalton's pioneering work in atomic theory was published in his book "A New System of Chemical Philosophy" in 1808.