Dichlorofluoromethane or Freon 21 or R 21 is a halomethane or hydrochlorofluorocarbon. It is a colorless and odorless gas. Its critical point is at 178.5 °C (451.7 K) and 5.17 MPa (51.7 bar). At temperatures from 5 K to 105 K it has one phase in the space group Pbca.
HMAS Melbourne (R21) was a ''Majestic''-class light aircraft carrier of the Royal Australian Navy (RAN).
R-phrases (short for risk phrases) are defined in Annex III of European Union Directive 67/548/EEC: Nature of special risks attributed to dangerous substances and preparations.
The R-21 (Р-21; NATO: SS-N-5 'Sark/Serb'; GRAU: 4K55) was a submarine-launched ballistic missile in service with the Soviet Union between 1963 and 1989.
The R21 was a New York City Subway car built by St. Louis Car Company from 1956 to 1957 for the IRT A Division.
The R21 / P157 is a major north-south provincial route (with a freeway portion designated as a National Road) in eastern Gauteng Province, South Africa.
The Renault 21 is a large family car produced by French automaker Renault between 1986 and 1994.
USS R-21 (SS-98) was an ''R''-class coastal and harbor defense submarine of the United States Navy.