Question

1. which of the following ideas was part of daltons atomic theory but has to be revised based on later discoveries?

all elements are composed of atoms.
atoms of different elements can combine in simple whole - number ratios to form compounds.
atoms of the same element are always identical (in mass and size).
atoms are neither created nor destroyed in a chemical reaction.
clear all

Explanation:

Dalton's atomic theory had postulates, and later discoveries (like isotopes) showed that atoms of the same element can have different masses (due to different numbers of neutrons). The other postulates (all elements have atoms, atoms combine in whole - number ratios, atoms are conserved in reactions) remain valid or are still foundational. So the idea that needed revision is that atoms of the same element are always identical.

Answer:

C. Atoms of the same element are always identical (in mass and size).