A reviewer has reviewed one of my papers. Recently, he mailed me and requested for a authorship in our new work. Is that ok? I am eager to know wether this would bring us academic misconduct if we give the authorship to him. Thank you so much!
This sounds like academic misconduct from his side. However, this depends on the exact circumstances. If you have been in contact with him in addition to the previous review and if he contributed something to your new work, you may add him as co-author.
If he requested authorship via authentic collaborations and contributions to the development of the new and related work and not authorship via sentiments, why not. In all cases, authorship must be earned via authentic contributions to a scientific work.
If he had an excellent contribution to improve your article, no problem at all, otherwise, it is shame to ask for that without doing any remarkable contributions. Regards.
If he/she or his/her comments helped you to improve your research, and you really think that his/her insightful comments worked, then there should be no issue.