Metals that are relatively rare in the earth's crust, difficult to extract, or found in low concentrations; used as essential materials in industries like aerospace, semiconductors, and nuclear energy.

Chemical elements that occur very infrequently in nature and are widely scattered; includes rare gases and elements such as selenium and tellurium, while the majority of others are rare metals

Group of chemical elements including helium, neon, argon, krypton, xenon, and radon; characterized by being colorless, odorless, and chemically inactive; formerly called [[惰性气体|惰性氣體|duo4 xing4 qi4 ti3]]