The Foreign Institutional Investors (FIIs) were net sellers to the tune of Rs 507.45 crore in the futures & option segment on Friday.According to data released by the NSE, FIIs were net sellers of index futures to the tune of Rs 178.93 crore and sold index options worth Rs 128.18 crore. They were net sellers of stock futures to the tune of Rs 195.91 crore and sold stock options worth Rs 4.43 crore.As per data available on the Sebi website - FIIs were net buyers of stocks worth Rs 191.50 crore in the cash market on Thursday. Mutual funds were net buyers of shares worth Rs 420 crore on the same day.