According to the law of conservation of matter, we know that the total number of atoms does not change in a chemical reaction and thus mass is conserved. The reactant in this model is hydrogen peroxide. Hydrogen peroxide decomposes to produce water and oxygen gas. How many water molecules must be added to complete this model?

The answer should be vaporization 

It is a mixture. simply put, a compound must be pure, that is, of only one chemical structure and composition. a mixture is made of different chemical substances (i.e. elements, molecules, compounds) that are not chemically bonded to each other, but instead physically grouped together, as in the case of gasoline (a homogeneous solution).

A. ​it generates energy from carbohydrates.b. it requires activation by oxygen.​c. ​it is used by cells to dispose of excess electrons