Hello

Mainly in  top colleges  Btech admission is done in as per entrance exam like JEE MAINS ,JEE ADVANCED some state entrance exams is also is also taken into consideration. Many college take their own entrance exam for admission in btech.

But don't lose your hope  some colleges may be take admission as per based. For that you have to contact college about details.

according to me for taking admission in top colleges you have to prepare for entrance exam .

I hope this helps you

Good luck