Computer Science and Engineering

With this rank, you can only join private colleges. You have an opportunity to get govt. colleges but not this branch. So, it's better to drop or go for private institutes like LPU, Thapar, LNMIIT, etc.

CSE will definitely give you high placement but it needs hard work and good study. In case of mechanical, you have to study less as compared to CSE, but in both the branches, you have to study more.

Apply for JoSAA counselling and choose the best IIT or NIT, among which you are getting admissions.
Kindly visit this link for top CSE engineering colleges from IITs and NITs:
https://www.shiksha.com/b-tech/ranking/top-computer-science-engineering-colleges-in-india/46-2-0-0-0

MANIT, Bhopal had a good placement record instead of the present scenario in most of the branches. Electrical being a core branch had less percentage placement and average package than CSE. Last year about 79% placement was recorded in MANIT for the electrical branch with the highest package of Rs 2

Go to freecodecamp.com and start developing from day one.

Yes, you can do, but it will not be beneficial for you. If you want to pursue masters, then you can go for M.Tech that will give you better career and scope in your field.

BIT, Jaipur is the extension center of BIT Mesra. I think you know about the importance of BIT Mesra, as a college for engineering. The degree is the same as for like the students of BIT Mesra main campus. The campus is not big which the only weak point is.
Placements in CSE are good enough. Compani

For CSE you should atleast have around 300 marks.