Hello omkar,

You need to opt for Science after 10th class, and need to clear examinations like JEE mains etc to get a good college of BTech or you have to score good marks in your 12th boards examination as well as  entrance examination for Bsc.

To become scientist in isro you need to score more than 65% or. 6.84 CGPA in BTech/ Mtech or bsc.if you get admission in Indian institute of space science and technology then it will be very easy for you to get a job in ISRO.

ISRO picks graduates from IITs and NITs directly, so you can go for these colleges as well.

Atlast you need to work hard, as the competition is high, but if you have passion then you will definitely get a job at ISRO.

I hope it helps,

Best of luck.