The foreign institutional investors (FIIs) were net buyers to the tune of Rs 799.58 crore in the futures & option segment on Monday.According to data released on the NSE website, FIIs were net buyers of index futures to the tune of Rs 420.94 crore and they bought index options worth Rs 156.92 crore. They were net buyers of stock futures to the tune of Rs 225.52 crore while they sold stock options worth Rs 3.80 crore.As per data available on the Sebi website - FIIs were net sellers of stocks worth Rs 53.50 crore in the cash market on Thursday. Domestic mutual funds (MFs) were net buyers of shares worth Rs 4.29 crore on the same day.