¿Has tratado de bucear? Means: Have you tried to snorkel? but Has is a informal way to say you. This is the better answer because is an informal question.
¿Ha tratado de bucear? Means: Have you tried to snorkel? but in a formal way, that doesn't feel good in that type of question.
¿Han tratando de bucear? Means: Have they tried to snorkel? is not the correct answer.
¿Hemos tratando de bucear? Means: Have we tried snorkel? Does not match the question.