What is the difference between Theoretical percent and experimental percent?

How can those two be applied to the following questions about my data?

False, as a substance changes from a solid to a liquid and from a liquid to a gas the molecules get farther apart from each other

The molar mass of a substance is defined as the mass of 1 mol of that substance, expressed in grams per mole, and is equal to the mass of 6.022 × 10 23 atoms, molecules, or formula units of that substance.

It will appear as o2(g) as a reactant