Citigroup agreed to acquire Knight Trading Group's derivatives markets business for $225 million in cash, according to news releases from the two companies. Knight's derivatives business includes trade execution services to institutions and broker-dealers for a significant number of U.S. options. It operates as a market maker and specialist in listed options on individual equities, equity indexes and fixed income and commodity futures. The acquisition is part of Citigroup's plan to expand its derivatives business, James Forese, Citigroup managing director and head of global equities, said in the release. The deal is expected to close in the fourth quarter.