Complete the sentence.
In this chemical reaction, oxygen is a ().

 - reactant
 - product
Read the underlined text carefully. Look for information about what happens to oxygen in this chemical reaction.
The Space Shuttle program sent astronauts on 135 missions using a fleet of five shuttles between 1981 and 2011. The engines of each shuttle, like other modern rocket engines, used liquid hydrogen as fuel. When liquid hydrogen combines with liquid oxygen, an enormous amount of energy is released, along with water vapor. The shuttles used this energy to launch into space.
The underlined text tells you that when hydrogen and oxygen combine, water is formed. When hydrogen and oxygen react, or go through a chemical change, their atoms are rearranged to form water. Because oxygen reacts in this chemical reaction, oxygen is a reactant.