The foreign institutional investors (FIIs) were net sellers to the tune of Rs 508.02 crore in the futures & option segment on Monday.According to data released by the NSE, FIIs were net sellers of index futures to the tune of Rs 425.45 crore while they bought index options worth Rs 16.98 crore. They were net sellers of stock futures to the tune of Rs 93.84 crore and they sold stock options worth Rs 5.72 crore.As per data available on the Sebi website - FIIs were net buyers of stocks worth Rs 152.10 crore in the cash market on Friday. Mutual funds (MFs) were net sellers of shares worth Rs 135.29 crore on the same day.