** Derivatives clearing firm StoneX Group's SNEX.O shares rise 4% to $78.55

** SNEX agrees to acquire futures brokerage R.J. O’Brien for $900 million in a cash-and-stock deal

** The deal, expected to close in the second half of 2025, comprises $625 million in cash and about 3.5 million shares of SNEX

** Transaction adds over 75,000 clients and strengthens SNEX presence in the derivatives clearing industry

** New York-based SNEX will also assume up to $143 million of RJO debt

** SNEX shares up 20% YTD

(Reporting by Arasu Kannagi Basil in Bengaluru)

((ArasuKannagi.Basil@thomsonreuters.com))