Like atoms are identical in all respects. This statement of Dalton’s atomic theory is contradicted. Which discovery contradicts this?

According to Dalton's atomic theory, the same atoms are identical in every aspect, but the discovery of isotopes contradicts these postulates. 

Isotopes have the same atomic number but different in mass which is a contradiction to Dalton's atomic theory. 

According to Dalton's atomic theory, the masses and densities of every atom in an element are the same. However, the atomic masses of certain element isotopes vary.

(For example: hydrogen, deuterium, and tritium).

The discovery of isotopes contradicts Dalton’s atomic theory.