Should water (h2o) be included in the model as a reactant or product? if so, how should it be included

yes we can.   a lady urinates from her urethra.

in a chemical reaction, the atoms and molecules produced by the reaction are called products. no new atoms are created, and no atoms are destroyed. in a chemical reaction, reactants contact each other, bonds between atoms in the reactants are broken, and atoms rearrange and form new bonds to make the products.

i think the answer is a.keratin is the pigment responsible for skin color.