Ar, or argon, is a colorless, odorless gas that is part of the noble gases group in the periodic table. It is the third most abundant gas in the Earth's atmosphere, making up about 0.93% of it. Argon is chemically inert, meaning it does not easily react with other elements, which makes it useful in various applications, such as in light bulbs and welding. Discovered in 1894 by Lord Rayleigh and William Ramsay, argon is often used in scientific research and industrial processes. Its non-reactive nature allows it to create a protective atmosphere for sensitive materials, preventing oxidation and contamination.