The foreign institutional investors (FIIs) were net buyers to the tune of Rs 128.21 crore in the futures & option segment on Monday.According to data released on the NSE website, FIIs were net sellers of index futures to the tune of Rs 75.27 crore and they bought index options worth Rs 109.90 crore. They were net buyers of stock futures to the tune of Rs 90.39 crore and they bought stock options worth Rs 3.19 crore.As per data available on the Sebi website - FIIs were net buyers of stocks worth Rs 131.20 crore in the cash market on Friday. Domestic mutual funds (MFs) were net sellers of shares worth Rs 79.55 crore on the same day.