The correct answers to test items should be kept secret and not revealed to anyone outside the test creators and scorers. This is especially important because people who have not found the solution to a difficult problem themselves but been given it lack the motivation for secrecy that comes natural to those who have solved it:
Someone who solves hard problems and receives a score for it will normally not want to help others of lesser ability to undeservedly score at that level, or above their true level, as that would reduce the meaning of the first person's own score. This constitutes the motivation for secrecy. But who receives the solution effortlessly, without having found it on one's own, will almost certainly abuse that information and pass it on to others, thus in one's own interest reducing the meaning of the scores of who are above one in ability. It is important that the second part of the previous sentence is well understood.
For this same reason, peer review in high-range psychometrics should remain limited to review of test contents (not answers) and statistics. Revealing the answers and explanations to reviewers will likely result in answer leakage through the psychological mechanism set forth above.