The foreign institutional investors (FIIs) were net buyers to the tune of Rs 51.30 crore in the futures & option segment on Tuesday.According to data released on the NSE website, FIIs were net sellers of index futures to the tune of Rs 0.20 crore and they sold index options worth Rs 19.66 crore. They were net buyers of stock futures to the tune of Rs 50.20 crore while they sold stock options worth Rs 18.36 crore.