Adding heat to a liquid causes which of the following physical changes?
a) increases mass
b) increases density
c) decreases density
d) no physical change

The density would decrease because the mass of an object deals with the amount of atoms in the object and since none of the object was reduced "a" wouldn't be the answer. Depending on the amount and period of time that the heat is applied the liquid could change into a gas so "d" wouldn't be correct. Density is the mass÷ volume, and when you add heat to an object it could take up different amounts of space because of its particles gaining energy and spreading apart. So the density would decrease because of the volume increasing. So I believe that "c" is the answer.