The main part of Dalton's atomic theory that was proven incorrect is the idea that atoms are indivisible and indestructible.

Here's a breakdown:

* Dalton's Theory: John Dalton proposed that atoms are the smallest unit of matter and cannot be broken down further.

* Discovery of Subatomic Particles: Later discoveries, like the electron by J.J. Thomson and the nucleus by Ernest Rutherford, showed that atoms are actually composed of smaller particles: protons, neutrons, and electrons.

* Nuclear Reactions: Nuclear reactions, such as nuclear fission and fusion, demonstrate that atoms can be split or combined, proving that they are not truly indestructible.

While Dalton's theory was groundbreaking for its time and laid the foundation for modern atomic theory, it was ultimately refined by further scientific exploration and discovery.