The Bombay Stock Exchange benchmark Sensex plunged by over 236 points to dip below 17,000 points level in opening trade on Monday as foreign funds and investors sold shares amid weakening global trends. The 30-share index fell to 16,898 points. All the sectoral indices were trading in the negative zone with losses up to 1.25 per cent. The wide-based National Stock Exchange index Nifty moved down by 72 points, to 5,011 points.