Oxygen Show clues again Liquid oxygen is often used as rocket fuel. Animals need oxygen to break down food and release the energy they need to live. Oxygen reacts with most elements to form oxides. Most of the rocks in the earth's crust are oxides.
Sea water contains water, salt and other minerals.
Water molecules are made from atoms of hydrogen and oxygen. Without oxygen, there can be no fire. The atomic number for oxygen is 8. O O 2 O 3 O 4 Oxygen exists in air in molecules of O 2 and O 3 . The air we breathe out contains more of a certain gas than the air we breathe in.