Hello,
The thing that differs RBI Grade B Exam from other banking exam is it's important to have 60% aggregate at 10th,12th and graduation level to appear for this exam, see the preliminary stage is same as that of any banking exam with quantitative aptitude, reasoning and english with general awareness,the tougher part line in the 2nd stage, so comparatively people from commerce/management background are well acquainted with all those concepts, for a beginner even though "economics and social science" is still manageable, but to learn those concepts of finance and management with the numerical that comes in exam isn't going to be easy,they have to put a lot of efforts to get the concepts clear and practice mock test on a regular basis in order to evaluate their progress. But, then not necessarily every person so far who've topped or succeeded this exam is necessarily from commerce/management background, there are always exceptions and if you want to give this exam, I'll definitely encourage you to go head, but first get your basics clear,there are lot of platforms in online medium who offer help,you may join it.

Hello,
RBI B Grade exam is conducted in November of every year. Application forms are out in 3rd week of September. It is 3 stage exam comprising of Prelims, Mains and Interview. There are about 200 vacancies every year.
The exam requires commerce and finance knowledge, so students with commerce background have a advantage.
However even a student of Science background can easily clear the exam with proper preparation, as the major portion of the exam is general studies based.

Follow this link for more information
https://www.google.com/amp/s/competition.careers360.com/articles/rbi-grade-b/amp

Good luck