The 30-share Sensex declined 161 points, or 0.21 per cent, to settle at 75,237.99, while the Nifty fell 46 points, or 0.19 per cent, to close at 23,643.50. Commenting on the technical outlook, experts said that 23,800 now acts as the immediate resistance level, followed by the crucial 24,000 psychological zone where Call OI concentration remains significantly high.