The correct answer is: unlikely.
The word “unlikely” means “not probable” or “not likely to happen”. In this context, it is unlikely that a mind so pure and searching could miss the truth. This is because a pure and searching mind is one that is open to new ideas and is constantly seeking knowledge. Such a mind would be unlikely to miss the truth, even if it was hidden or difficult to find.
The other options are incorrect because they do not accurately reflect the meaning of the sentence. The word “likely” means “probable” or “expected to happen”. In this context, it is not likely that a mind so pure and searching could miss the truth. The word “possibly” means “there is a chance that something might happen”. In this context, there is a chance that a mind so pure and searching could miss the truth, but it is not very likely. The word “scarcely” means “almost not at all”. In this context, it is almost impossible that a mind so pure and searching could miss the truth.