The Foreign Institutional Investors (FIIs) were net buyers to the tune of Rs 1,840.87 crore in the futures & option segment on Monday.According to data released by the NSE, FIIs were net buyers of index futures to the tune of Rs 1,471.80 crore and bought index options worth Rs 333.96 crore. They were net buyers of stock futures to the tune of Rs 30.69 crore and bought stock options worth Rs 4.42 crore.