Helium is a member of the group known as "rare" gases and has no colour, odour or taste. Helium is the second lightest element, one-seventh as heavy as air. It is chemically inert, has low solubility in water and cannot be made to burn or explode. Helium is the coldest known liquid at -269 °C.
Although it is the second most abundant element, helium is difficult to come by. Most helium gas is extracted from natural gas sources containing from 1% to 7% helium by volume. These types of natural gas deposits are rare and are mainly found in certain areas of the United States, Canada, Poland, Russia, and Africa.
Helium's applications mainly utilize its cold, inert or buoyant properties. As a cooling agent, helium is used in basic scientific research, medical imaging (NMR) and various analytical or production processes. Helium is also used in welding and cutting applications and in laser applications. Leak detection, deep sea diving and balloons also rely on helium's special properties.