Final answer:
Water can put out fires due to its properties as a stable compound that is not flammable and absorbs heat, resulting from the exothermic reaction between hydrogen and oxygen.
Step-by-step explanation:
The reason why water, which is composed of hydrogen and oxygen, can extinguish fires despite hydrogen being flammable and oxygen supporting combustion lies in the property of chemical reactions. When hydrogen (H₂) and oxygen (O₂) react to form water (H₂O), the process is a highly exothermic reaction, releasing a significant amount of energy and resulting in a stable compound with different properties than the individual gases. Unlike the explosive nature of hydrogen or the combustion-supporting property of oxygen, water is not flammable and actually absorbs heat, thus reducing the temperature and separating the fuel from oxygen in the air, which helps to put out fires.