The Foreign Institutional Investors (FIIs) were net buyers to the tune of Rs 578.94 crore in the futures & options segment on Tuesday.According to data released by the NSE, FIIs were net buyers of index futures to the tune of Rs 546.60 crore and bought index options worth Rs 166.95 crore. They were net sellers of stock futures to the tune of Rs 124.58 crore and sold stock options worth Rs 10.03 crore.