Any of a group of six chemical elements namely helium, neon, argon, krypton, xenon and radon. They are colourless and odourless natural gases found in the atmosphere. The noble gases were discovered in the 1890s by the British scientists Lord Rayleigh and William Ramsay. They are called noble because they do not easily react with other elements. All of them except radon, which is highly radioactive, are used in incandescent and gas-discharge lamps. Argon and helium are used in welding. Helium is also used in balloons that carry scientific instruments high into the atmosphere. Radon is at times used in cancer treatment because of its radioactivity.
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