Hey! There's no set number- it depends on what type of research you are doing and how broad your research questions are. In my thesis introduction I outlined 5 broad research questions, but within those questions there were another 3-4 specific questions that were outlined in the individual chapters. I don't know what subject you're in, but in the sciences it's common to aim for about 3-4 results chapters, so you need to think about what results you will have and how you will report them! Best, KB