are: the gaseous chemical elements helium, neon, argon, krypton, xenon and radon, whose molecules consist of single atoms. [P8.4]
are placed: in a group of the periodic table. [P8.4]
are so-named: because of their marked reluctance to 'lower' themselves by combining with other chemical elements to form compounds. [P8.4]
are also called: inert gases.
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