Concept:The right to buy or sell a security at an agreed price within a fixed time is called an option.Explanation:An option is a financial contract that gives the holder the right, but not the obligation, to buy or sell an asset before a stipulated expiry date.Thus, the correct term for this right on the stock exchange is an option.Contango and backwardation refer to price differences in futures trading, not direct buy-sell rights.Brokerage is the fee charged by a broker for executing transactions, not a trading right.Answer:A. option