Is c4 a compound element or mixture

Iam in desperate need of with this !

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?

What are transitions between a liquid and a solid called? identify which way they are transitioning