Which theory belongs in place of the question mark in tran’s timeline?

Assuming that the timeline that you're referring to is in the year of 1803, the theory is probably belong to Dalton
In 1803, John Dalton proposed a theory that would change the field of chemistry for the rest of the time, which is the discovery of atom

hope this helps

Idk sorrry( it’s hard and u only gave a little points we need more points if u want help):