Reviewers had questions about why my supervisor wasn't on manuscript I completed my MS by research under a supervisor. There was considerable delay in completing because my supervisor suddenly lost interest in research midway through my program. I had sent him a research paper for his comments but even after several reminders, he did not show interest in looking at the paper. After graduating from the program, I decided to send it to a journal myself. I sought permission from my supervisor and he was ok with it. Since he had not reviewed it, he said he could send it without including his name as one of the authors. So, I had acknowledged his guidance in the paper in the acknowledgement section. I had sent the paper and now, in the reviewer comments, one of the reviewers has asked about not adding the supervisor's name in the author list (it was listed under minor comments). I'm not sure how to respond to this question. Right now, I'm not exactly on speaking terms with my supervisor. Can anyone please help me?
Just reply with the facts: Explain that your supervisor was offered coauthorship, but has chosen not to be a coauthor of the paper.  (If you feel you want to elabore why - e.g. since he felt he did not contribute sufficiently to the paper, or the like - feel free to do so.)
Especially if this is listed under minor comments, take it as such.
In any case, it is generally not up to the referee to judge who should be a coauthor of a paper. What can be demanded is that you offer coauthorships to anyone who made a significant enough contribution to the paper. As long as you did that, you are fine.