Temperature is a measure of how much the atoms in a substance are moving. why is a substance hotter in the gas state than in the liquid state?

Because the only way to get a gas is to heat up the atoms. It is a gas because of the movement of its atoms. They are capable of freely moving around because the bond that holds atoms together in a liquid or solid ceases to exist, as it only holds atoms in cooler conditions.

I think.

A) acceleration. this seems to be the one that makes sense.