The Sensex at the Bombay Stock Exchange closed with a small loss of 21 points, or 0.1 percent, at 17,131, after volatile trade, on the expiry of the monthly derivatives contracts, on Thursday. The Nifty at the National Stock Exchange lost 13 points, or 0.3 percent, to 5,189.Stock markets in Hong Kong, South Korea and Singapore rose between 0.1 percent and 0.8 percent.