The Sensex at the Bombay Stock Exchange declined 42 points, or 0.3 percent, to 16,805, on profit-booking by investors on Monday. The Sensex had gained more than 840 points in the last three trading sessions.The Nifty at the National Stock Exchange fell 11 points, or 0.2 percent, to 5,039.Stock markets in Japan, China, Hong Kong, South Korea and Singapore ended mixed.