Chemistry

It also depends on interest. If you are very passionate for law then LL.B. would be a good option. Although LL.B. is a regular course but in few government law colleges and affiliated private law colleges it proceeds at very easy going pace which can give you a chance to do part time or online jobs like content writing or BPO. M.Sc. Chemistry would take your 2 year. LL.B would be a new subject but can give you wings for lifetime advocacy. If interested in teaching M.Sc. Would be a better choice. Thus, I suggest you to go for that field in which you can do better or which is your area of strength.

You are eligible to give CAT exams which will further decide whether you make into IIM or not. CAT exam is the 1st screening step to get into the IIM. To write CAT exam the minimum eligibility criteria is 50% and above in graduation, 12th and 10th. So yes you are eligible to write CAT exam and depending upon the scores you get in this exam you have to apply into the Iims of your choice and score for further selection process.

It depends on which course you want to do. But still for most of the courses only marks in PCB are taken into consideration.