Hello Kamalaksh!

Mechanical engineering would be a suitable choice for you considering your preferences. First you can go for B.Tech Mech engineering and then M.Tech Aerospace engineering. Mechanical engineering specializes broadly in robotics and mildly in aeronautics. Take aerospace engineering or avionics as a specialization whike B.Tech MechE and you will get what you need. But in B.Tech Aerospace engineering, you can not find much scope to expertise in robotics in India.

So in my opinion, a B.Tech degree in Mechanical engineering will be suitable for you to find jobs and research in robotics and mechatronics field. Then, if you wish to find jobs in aerospace field, you can find one after M.Tech/M.S in Aerospace engineering. But if you go for Aerospace engineering, your job and research opportunities will be limited only in aerospace related area.

Hope you are clear!