What is true of a molecule? a. each molecule of a substance has different properties b. all molecules of a substance have the same properties c. all molecules of a substance have one type of atom d. each atom of a molecule is the same size

The correct answer is that all molecules of the same substance have the same properties - because they are composed of the same kinds of atoms. 

Atoms of different pure substances (such as the ones from the periodic table) have different sizes - so not all atoms are equal. But all molecules of water, which is a substance is always composed of two hydrogen atoms and one oxygen atom- that gives all the molecules the same properties. 

It changes food into energy that the organism can use.