IIT Indore - Indian Institute of Technology

In my opinion, you should opt mechanical from IIT-Indore because IIT-Indore provides good mechanical faculties, good course curriculum, good placements and good infrastructure also.

IIT-Roorkee for chemical engineering due to its academics and placements.

In my opinion, you should opt for mechanical engineering in IIT-Indore because IIT-Indore has experienced mechanical engineering faculty members and good course curriculum.

First of all, I am very sad to say that with such a percentage, you cannot think of getting admission for B.Sc in astrophysics. This field demands a percentage of 80% or above. If you want to fulfill your dream, please go for 12th improvement examination though its a very tough decision to take think twice what you want from yourself. If you have very strong determination regarding this prospect, please go with it. God with and you yourself will definitely help! Looking forward for your reply with your decision to guide you further. Good luck.
I keep a strong faith on you!

You can check the this year's category wise opening and closing ranks of various IITs at
http://jam.iitb.ac.in/round_3.pdf
and for more information about IIT JAM, visit:
http://jam.iitb.ac.in
Best of luck.

Hi Sarjeet, Candidates must have a Bachelor's degree in Physics or Mathematics or CSE or EE or ME. Minimum Eligibility to Apply: 55% graduation. For further details, refer below
https://www.shiksha.com/science/course/m-sc-in-astronomy-indian-institute-of-technology-Indore-291586.

Yes, elective subjects are not considered to be that much of important so you can choose any branch.