The Russian Soviet Federative Socialist Republic (Russian SFSR or RSFSR; Russian: Российская Советская Федеративная Социалистическая Республика, tr. Rossiyskaya Sovetskaya Federativnaya Sotsialisticheskaya Respublika  listen (help·info)) commonly referred to as Soviet Russia or simply as Russia, was a sovereign state in 1917–22, the largest, most populous, and most economically developed republic of the Soviet Union in 1922–91 and a sovereign part of the Soviet Union with its own legislation in 1990–91. The Republic comprised sixteen autonomous republics, five autonomous oblasts, ten autonomous okrugs, six krais, and forty oblasts. Russians formed the largest ethnic group. To the west it bordered Finland, Norway and Poland; and to the south, China, Mongolia and North Korea whilst bordering the Arctic Ocean to the north, the Pacific Ocean to the east and the Black sea and Caspian Sea to the south. Within the USSR, it bordered the Baltic republics (Lithuania, Latvia and Estonia), the Byelorussian SSR and the Ukrainian SSR to the west. To the south it bordered the Georgian, Azerbaijan and Kazakh SSRs.
Try to answer this question if possible (otherwise reply "unanswerable"): When did the RSFSR cease to be a part of the Soviet Union?
91