Indian stock markets closed lower on Monday, with the Nifty 50 falling below 26,000 and the Sensex dropping 441 points. Broad-based selling intensified in the final hour, driven by anticipation of monthly derivatives expiry. While auto stocks outperformed, defence and real estate sectors faced significant pressure. Midcap stocks like RVNL and NBCC showed resilience, bucking the overall negative trend.