Question

what did john dalton propose in 1803?
he theory of relativity
the existence of noble gases
the periodic table
atoms were at work in chemical reactions

Explanation:

John Dalton's 1803 work centered on atomic theory, which established that atoms are the fundamental units involved in chemical reactions. The theory of relativity was proposed by Einstein, the periodic table by Mendeleev, and noble gases were identified later by other scientists.

Answer:

D. Atoms were at work in chemical reactions