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a trademark that is officially or legally certified by a government, as the U. S. Patent and Trademark Office
Product wrappers and business documents often indicate that a trademark is registered by adding TM (for ‘trademark’) or R (for ‘registered’) in a superscript circle after the term.
radical (usually an alkyl or aryl group)
respiratory exchange ratio
or r roentgen
Abbreviation of radius
The symbol for resistance.
unit of X-radiation or gamma radiation, the amount that will produce, under normal conditions of pressure, temperature, and humidity, in 1 kg (2.2 lbs) of air, an amount of positive or negative ionization equal to 2.58104 coulomb. It is named for the German physicist Wilhelm Conrad Rontgen. See also rem.