Which of the following statements is incorrect?
a. the only way to determine the products of a reaction is to perform the reaction.
b. all chemical reactions can be classified as one of five general types.
c. a single reactant is the identifying characteristic of a decomposition reaction.
d. complete combustion has occurred when all the carbon in the product is in the form of carbon dioxide.
(i was thinking b.)

A. The only way to determine the products of a reaction is to perform the reaction.

Explanation:

Even with the reactants, you can predict the products of a reaction without performing it.  You can spot the active functional group in the reactants, classify them as electron donor, acceptor or radical. Then use your basic knowledge of balancing an equation; and how the reactants would interact with one another to end up with one or more possible structure(s).