Falling for the third straight session, the Sensex at the Bombay Stock Exchange slumped 343 points, or 2.1 percent, to close below the 16,000 level, at 15,870, on Monday, after negative industrial output numbers, and amid weak European markets. The Sensex had had already lost more than 660 points in the past two trading sessions. The Nifty at the National Stock Exchange declined 102 points, or 2.1 percent, to 4,765.Stock markets in Japan , China , Hong Kong , South Korea and Singapore ended mixed.