The foreign institutional investors (FIIs) were net buyers to the tune of Rs 392.25 crore in the futures & option segment on Tuesday.According to data released on the NSE website, FIIs were net buyers of index futures to the tune of Rs 254.74 crore while they sold index options worth Rs 50.21 crore. They were net buyers of stock futures to the tune of Rs 186.10 crore and they bought stock options worth Rs 1.61 crore.