Consider the unbalanced equation for the oxidation of butene.

C4H8 + 6O2 CO2 + H2O

For each molecule of C4H8 that reacts, how many molecules of carbon dioxide and water are produced?

Balance the equation to find the answer. The easiest place to start is with the C's and H's since they only appear once on both sides of the equation:

C4H8 + 6O2 - > 4CO2 + 4H2O

The O2 has already been balanced for us (but normally you would add the number of O's on the right after balancing C's and H's and use that to balance the O's on the left).

As you can see you get 4 molecules of CO2 and 4 of H2O.