A chemical change in which a single compound is broken down into two or more simpler products.

Decomposition or cracking

Explanation:

Decomposition reaction is a chemical change in which a single compound is broken down into two or more simpler products.

  For example;

                   A     →    B   +  C

 The driving force of such reaction is the high positive heat of formation of the compound which indicates that they are highly unstable.

Some stable compounds also decompose when subjected to high temperature and pressure.

if you mean hydrogen and oxygen then water is the product