The Foreign Institutional Investors (FIIs) were net buyers to the tune of Rs 531.28 crore in the futures & option segment on Thursday.According to data released by the NSE, FIIs were net sellers of index futures to the tune of Rs 15.15 crore while bought index options worth Rs 452.40 crore. They were net buyers of stock futures to the tune of Rs 94.25 crore while sold stock options worth Rs 0.22 crore.As per data available on the Sebi website - FIIs were net buyers of stocks worth Rs 520.20 crore in the cash market on Wednesday. Mutual funds were net sellers of shares worth Rs 206.79 crore on the same day.