Final answer:
Dalton's atomic theory stated that atoms could be combined to form compounds, which remains true today, despite revelations that atoms can be subdivided and transformed into other atoms via nuclear reactions. (Option A).
Step-by-step explanation:
John Dalton's atomic theory, proposed in 1804, set the foundation for our understanding of matter and its composition. Dalton's theory centered on the idea that all matter is made of small, indivisible particles called atoms, which are involved in chemical reactions where they are rearranged, combined, or separated but not destroyed or turned into other atoms.
However, modern advancements have led to three significant changes to the theory: (1) atoms can be subdivided into subatomic particles, (2) atoms of the same element can have different masses due to isotopes, and (3) through nuclear fission and fusion, atoms can indeed be converted into atoms of other elements.
Therefore, when Dalton stated that atoms could be 'combined to form compounds', he was partially correct. Atoms of different elements can join in specific whole-number ratios to create compounds, which is still acknowledged in modern chemistry, even though we now understand the additional complexity of atomic structure and transformations that Dalton's theory did not cover. (Option A).