The 30-share Sensex fell for fourth day in a row and Nifty 50 index closed below its important psychological level of 18,600 after the Reserve Bank of India hiked key interest rate by 35 basis points taking the repo rate to 6.25 per cent. The RBI's Monetary Policy Committee delivered its fifth straight increase as inflation remains elevated, and the central bank says that there will be no let up in flight to tame inflation.