Oxygen is a tasteless gas. It has no smell or color. It comprises 22% of the air. Major applications:

• Industries use the gas for cutting, welding and melting metals. The gas is capable of   generating temperatures of 3000 C and 2800 C. This is required for oxy-hydrogen and    oxy-acetylene blow torches.

• In healthcare institutions like hospitals, oxygen supplies are kept in stock. These are provided   to patients who have difficulty breathing. This breathing apparatus is also used by astronauts   walking in space, scuba divers and mountaineers.

Nitrogen is a non-reactive gas. It has no color, odor or taste. It comprises around 78% of the Earth’s atmosphere. Major applications:

Helium is the second lightest elemental gas next to hydrogen. The smallest of all molecules, it has the lowest boiling point of any element. It is chemically inert and non-flammable, only slightly soluble in water and has high thermal conductivity. Helium is used for many applications including:

• Creating an inert gas shield and to prevent oxidation during welding of metals such as    aluminium, stainless steel, copper, and magnesium alloys.

Argon is the third most common gas in the Earth's atmosphere, at 0.93%. Application:

• Mostly used as an inert shielding gas in welding and other high-temperature industrial    processes where ordinarily non-reactive substances become reactive

• Argon in combination with Carbon dioxide forms Argo-shield gas which produces a stiff arc   with a broad heat flow. Can be used in a wide range of applications from light to medium plate   fabrication, structural steel works, bridgework, vehicle manufacture and   general fabrication

This is an explosive gas which in the pres­ence of the right amount of oxygen burns with a brilliant flame at a temperature of about 3000°C. Application:

• Oxy-acetylene blowtorch is widely used in welding and cutting metals with high melting    points and this forms almost the sole use for the gas.