Oxygen is an element. This substance is normally found as a gas. One-fifth of the air around us is oxygen. Oxygen is particularly important for humans and animals: you need it to breathe.
For a long time, people only knew the air. In the 18th century, however, it was understood that it consists of several substances. Oxygen often plays a role when something is burning in a fire. Then elements combine with oxygen. This also happens with rusting: iron slowly absorbs oxygen, and rust is actually a combination of iron and oxygen.
Oxygen is the most common element on earth. It’s not just in the air: rock and sand contain oxygen. Water consists of hydrogen and oxygen.
The item has no color and no odor. If you make it very cold, it becomes liquid or even solid. It then consists of blue crystals.