Explain how the four states of matter differ at the molecular level

In solids, strong bonds between atoms/molecules keep them in place. There is not much movement of the individual particals. If you add heat, your substance will go through the different states of matter because the energy you put in is enough to break these bonds between particles. Plasma is a bit different. These are just gas particles BUT they have a charge (that can move from one particle to another) which causes electricity.

It would be true sodium reacts with water in a violent way 

In any atom of any element, you will find protons and neutrons in the nucleus of any atom