Posting its biggest single-day gain in three months, the Sensex at the Bombay Stock Exchange jumped 265 points, or 1.4 percent, to close above the 19,000 mark, at 19,143, today, on hopes of more measures to boost economic growth, and amid a rally in the global markets. The Nifty at the National Stock Exchange rallied 86 points, or 1.5 percent, to 5,784.Stock markets in Japan, China, Hong Kong, South Korea and Singapore gained between 0.1 percent and 2.3 percent.