The English scientist John Dalton were one of the early scientists who paved the way to science, particularly in atomic chemistry. His atomic theory jumpstarted further developments made by J.J Thomson, Rutherford, Bohr, Schrodinger and many more.
Dalton's atomic theory can be summarized in 5 key points:
1. Atoms are tiny, indivisible and indestructible particles of an element.
2. Atoms of different elements vary in size and mass.
3. Atoms of an element are uniform in size and mass.
4. Compounds are formulated by a fixed ratio of individual atoms of elements.
5. Reactions undergo by rearranging the atoms of the reactants to form the products.
From the choices, the acceptable answer would be: The ratio of atoms in a compound is fixed.