About two thirds of the human body, and nine tenths of water, is oxygen. The gas is colourless, odourless, and tasteless. Liquid and solid oxygen are pale blue and strongly paramagnetic. Aerosols in the atmosphere have a detrimental effect on the ozone layer. Large holes in the ozone layer are forming over the polar regions and these are increasing in size annually.
Undiluted ozone is bluish in colour.
Oxygen is very reactive and capable of combining with most elements. It is essential for respiration of all plants and animals and for practically all combustion. Both values are quoted on the Pauling scale. For most elements, the most stable allotrope is illustrated. This section gives some data for naturally occurring isotopes.