In Mark 10, Jesus said a husband and wife are no longer two but what?

Answer: One flesh

Quoting Genesis, Jesus said the two become one flesh, so what God has joined together man must not separate.

“‘For this reason a man will leave his father and mother and be united to his wife, and the two will become one flesh.’ So they are no longer two, but one flesh. Therefore what God has joined together, let man not separate.””— Mark 10:7-9 (BSB)