Scientists initially believed that the smallest particle of matter was the atom. then, particles smaller than the atom were discovered. what most likely contributed to the change in this theory?

The correct answer will be- the advancement in the technology

Explanation:

The atomic theory which suggested that atom is the smallest and indestructible form was proposed by the John Dalton in 1803.   Later the atomic theory was modified with the discovery of the sub-atomic particles like electrons, protons and neutrons.

This modification in the theory is the result of the advancement in the technology which provided new evidence of the atomic models which represented the distribution of the sub-atomic particles in the atom.

Thus, the advancement in technology is the correct answer.