Appearance
Oxygen is a colourless, odourless, tasteless gas

Source
Oxygen forms 21% of the atmosphere by volume from which it can be obtained by liquifaction and fractional distillation. The element and its compounds make up 49.2% by weight of the Earth's crust. About two thirds of the human body and nine tenths of water is Oxygen. In the laboratory it can be prepared by the electrolysis of water or by heating Potassium chlorate with Manganese dioxide (Manganese (IV) oxide) as a catalyst.

Uses
Oxygen is very reactive and capable of combining with most other elements. It is a component of thousands of organic compounds, and is essential for the respiration of all plants and animals and for almost all combustion.

The greatest commercial use of gaseous Oxygen is Oxygen enrichment of steel blast furnaces. Large quantities are also used for making synthesis gas for Ammonia and Methanol, Ethylene oxide and for oxy-acetylene welding.

General Information
The liquid and solid forms of Oxygen are pale blue in colour and strongly paramegnetic. Ozone is a highly active allotropic form. The presence of an Ozone layer in the atmosphere (equivalent to 3mm thick at normal temperatures and pressures) prevents ultra-violet rays from the Sun from reaching the surface of the Earth. The use of some aerosol propellants has reduced the thickness of this layer.