The Foreign Institutional Investors (FIIs) were net buyers to the tune of Rs 511.31 crore in the futures & option segment on Thursday.According to data released by the NSE, FIIs were net buyers of index futures to the tune of Rs 406.59 crore and bought index options worth Rs 183.21 crore. They were net sellers of stock futures to the tune of Rs 90.11 crore while bought stock options worth Rs 11.63 crore.As per data available on the Sebi website - FIIs were net sellers of stocks worth Rs 46.60 crore in the cash market on Thursday. Mutual funds were net buyers of shares worth Rs 80.20 crore on the same day.