Hi Snigdha,

To take admission in top most engineering colleges for B.tech you have to score at least 60% in 12th board so that you will be eligible to give the entrance exam and if you are aiming for NITs or IITs or any IIITs then you should must score at least 75% in boards.

After that you have to give entrance exams for different colleges like:-

BITSAT,COMEDK,WBJEE,VITEEE,UPESEAT,KCET(for Karnataka student) and many other private universities takes their own exams.

Hope this will help,please feel free to ask if you have any further queries.

Thank You.