Question

The Atomic Theory offers an explanation of a small particle of matter, called the atom. What must be true for a scientific theory, such as the atomic theory, to be strong and well supported?

Answer 1

If experiments can't falsify the theory then we most except the theory is strong according to the theory of science from Karl Popper (the falsifiability criterion), or said in another way:
Every "good" scientific theory is a prohibition: it forbids certain things happen. The more a theory forbids, the better it is.

Answer 2

for the atomic theory to be accepted is the smallest particle are the neutron,proton and electron