What was the largest dinosaur ever to live? did it live in the water or land?

Well, "Sea Dinosaurs" never existed, only marine reptiles like the Mosasaurus or Elasmosaurus, so no dinosaurs ever lived in the sea, but the largest dinosaur would be the Argentinosaurus, a sauropod, AKA a "Long Necked Dinosaur"

The Argentinosaurs was 100 feet long and 55 feet tall, weighing in at about 120 tons!