Sensex plunges 236 pts: Hurtling down for the third straight day, the benchmark BSE Sensex on Tuesday broke below the crucial 28,000-mark, a fall of over 235 points, amid lacklustre corporate earnings numbers. This was its lowest closing in nearly two weeks. Investors' appetite took a hit over the gridlock in Parliament about the key GST Bill and global volatility after a devaluation of the yuan, brokers said.