Hey aspirant, Your overall percentage in 12th Board is considered in Jee mains and Physics, Chemistry and Maths are required to be the main subjects in 10+2.

You must score 75% or more in 10+2 for being eligible for admissions in most of the NITs and IIITs.

Also, you must be doing or have passed 10+2 from any recognised board.

Hope this helps.

For further doubt regarding this please ask in comments.