Someone please help me! I only have about 10 mins please I will mark you as brainlist

There are main groups in the modern periodic table of elements

In the 1800s, one of the statements in john dalton's atomic theory was that atoms are indivisible. later experimental evidence led to the discovery of subatomic particles such as neutrons, electrons, and protons. what happened to the indivisible atom part of dalton's atomic theory, and why?

Significant figures are digits read directly from the measuring instrument plus one more digit, which is __ by the observer.