2H2O _> 2H2 + O2

Look at the chemical equation above. What is the purpose of the coefficients ?
A.
These coefficients show how many particles of each substance are used in the reaction.
B.
These coefficients show how many atoms of product will be formed during the reaction.
C.
These coefficients show how many substances are used in the reaction.
D.
These coefficients show how many elements are used in each chemical formula.