The primary difference cannot be color. Why? just because you move from one state to another it doesn't mean it will change colors. Anyways, this isn't a PRIMARY difference, although it can be true.
The mass of the substance CANNOT be changed. Why? Well, according to the law of conservation of mass, mass cannot be created nor destroyed. Not a primary difference.
Number of atoms in the substance cannot change PHYSICALLY, but the number can change CHEMICALLY. Out of the picture!
last but not least, the amount of movement of atoms in a substance is the primary difference between the states of matter. Plasma has super fast atoms that are going in random directions everywhere, and they are spread out, just like the gaseous state. Liquid state has atoms that slide past one another, fill up the container they are in, and are more tightly packed but are still somewhat loose. In a solid, the atoms are moving ever so slightly and they are completely packed and firm, which is why if you hit your table right now it won't melt around your hand (and why it is standing...). Then the last state of matter, the bose-einstein condensate, pretty much reducing the temperature to absolute zero, is when molecular motion is pretty much stopped.
To the point: <u>The amount of movement of atoms in the substance is the primary difference between the states of matter!</u>
