a. The reactant side is the left side of the reaction. So, by looking at CH4, there is 1 Carbon atom and 4 Hydrogen atoms. And in 2O2, there are 2*2=4 Oxygen atoms.
b. The right side is the products. There is 1 Carbon, 2*2=4 Hydrogen, and 2+2*1=4 Oxygen.
c. The reaction is balanced because the total number of C,H,and O in the products and reactants are the same.
d. The coefficient 2 in front of H2O means there are 2 of that molecule in the balanced reaction.
