Hello,

The eligibility criteria to appear for UPSC CSE is passed graduation in any discipline from a recognized university, hence there is no such restrictions of belonging to specific stream, now coming to your question if you're enquiring about BSc Hons Chemistry being useful from the perspective of preparation of the exam, then there is optional paper of UPSC having this subjects, apart from the syllabus of UPSC itself is more inclined towards humanities subjects such as history, geography, economics, polity etc, the portion of science isn't that much, however if you have any other plans for future than appearing for UPSC, you should go ahead with your choice for BSc Chem Hons, the reason being UPSC is highly competitive exam, and it's good to have a back up plan, also you have just passed 12th, and you're still in a phase of figuring out your career plans, it's quite natural if you're not absolutely sure of only appearing for UPSC,

secondly I want to emphasize again that irrespective your stream at 10+2 or graduation level, you can qualify this exam is you have single minded focus, dedication and perseverance, if you look at previous year toppers they come from as diverse backgrounds as engineering, medical, science, commerce, etc, so there is no absolutely no reason why you cannot qualify you give all your efforts in this exam, as I said the attributes which make one successful in this exam are how focused, dedicated, and consistent you are in your efforts, and this holds true for every aspirants.