More precisely, is “No, it is not” a correct answer to this question?
If it is a correct answer, then by the meaning of “No, it is not” that answer is not a correct answer. And of course, it cannot be correct and not correct; the meaning of “not” rules that out. But, if it is not a correct answer, then “No, it is not” would be a correct answer to our question. Could it be the case that there is no correct answer? But then “No” would still be a correct answer to our question. We therefore need a correct answer. Now, if “No, it is not” was as correct as not, then it would be as incorrect as not, which would solve our problem; and since we have ruled out all the other sorts of answers, hence that does solve our problem. A good answer to our question is therefore: It is as correct as not.
You may be wondering: Can answers be as correct as not? Another reason why they must be able to be comes from the following question: Is “It is an apple” a correct answer to the question “What is A?” where A is originally an apple but has its molecules replaced one by one with molecules of beetroot? Originally it is a correct answer, but eventually it is not, and so if it must be either correct or else not, then an apple could be turned into beetroot by replacing just one of its molecules with a molecule of beetroot. But of course, that is not what “apple” means.