Which is the correct adverb?

Wrongly, as it modifies the verb guess. Nevertheless, many native-speakers would say or write "wrong."

Thanks, Setanta.

I was surprised by the fact that some native speakers use "wrong".

A great many native-speakers don't "follow the rules." That's how languages work, though. Most people are intelligent, and they understand what people mean--it is also, at least among Americans, considered ill-mannered to correct people when they speak. Your question a few days ago provides a good example of how people can understand their own language, even when used in an unfamiliar manner. Using ward as a verb to mean hospitalizing someone is something I had never seen before--but I knew right away what was meant. If you were to correct an American's speech, he or she would probably say something like: "Well, you knew what I meant, didn't you?" It would be said with some asperity.

In conversation I would naturally say, "You guessed incorrectly", but I find I have to force myself to say, "You guessed wrongly." It's perfectly correct but it sounds "off" to me.

I think I would say... "You got it wrong." But then "wrong" is an adjective.

You and Henning Wehn. He's a German comedian describing how his grammatically correct, school learnt English is at odds with that spoken in London.



There's also an anti intellectualism side to this, deliberately using the wrong verb forms to make a point.

You just say, 'Guess again'.