Snapping a five-session rally, the Sensex at the Bombay Stock Exchange dropped 211 points, or 1 percent, to close at 20,091, today, with sentiment dampened after the Reserve Bank announced additional liquidity tightening measures to check the rupee's slide. The Nifty at the National Stock Exchange fell 87 points, or 1.4 percent, to 5,991.Stock markets in Japan, China, Hong Kong, South Korea and Singapore ended mixed.