O2 is oxygen. 

Oxygen is a simple substance, in the chemical properties of the more active type, but in the room temperature environment is not active. Many different elements can react with oxygen, and with the exception of a few rare gases, compounds produced by the reaction of different elements with oxygen are called oxides.

But in the air, oxygen is constantly replenished by photosynthesis with plants. Oxygen is generally a colorless, odorless gas. It exists in one of the most common elemental forms of oxygen. It is not easily soluble in water and can dissolve about 30 milliliters of oxygen in 1 liter of water. It is widely distributed in nature and makes up about 48 percent of the earth's crust.

What are the benefits of o2?

First: has an important role in chemistry, many different elements and oxygen after the occurrence of a lot of different reactions of the compound, at the same time in the process of doing scientific research occupy an important gas;

Second: in medical treatment, patients with hypoxia can provide breathing, life support, provide medical rescue;

Third, it provides oxygen for human needs in diving operations and aerospace.

Fourth: In the process of smelting, oxygen with high purity is needed to react with other elements, which can reduce the carbon content in steel and remove many impurities. In addition, enough high-purity oxygen is needed in the process of oxidation reaction to maintain the continuous temperature required by refining. The use of high purity oxygen in individual metal smelting process can also greatly shorten the smelting time.