What must models and theories do in order to remain valid

- "the choice that is not an indicator of a chemical change is "state of matter changes". more common than not, chemical reactions produce energy in the form of light or heat. along with energy, they also produce a new substance called the product that could be in any state of matter (solid, gas, or liquid)."

i believe you are right for all except the 3rd ( look at sqdancefan his answer is much better)