Oxygen is a colourless gas which is non-explosive. It is also tasteless and odourless in nature. It is the most abundantly found gas on earth. Oxygen enters into human body through the process of respiration and occupies two third of human body. Oxidation is a reaction that occurs when oxygen gets combined with other substances. Substances burn in air due to the presence of oxygen. Oxygen is essential for breathing in humans and life support is possible only through its presence.