Mumbai: The BSE Sensex on Thursday dropped 1625 points at 55,606.53 in the opening session after Russia ordered a military operation in Ukraine.The Nifty too slid 482 pts at 16,580.80.The Sensex registered days high and low at 55,996.09 and 55,147.33 pts respectively.The Nifty registered days high and low at 16,705.25