I failed in chemistry in 12 class so Can i do btech/be with only math and physics
It's not possible.
As you have failed in chemistry in class 12 , you need to clear it to become eligible. It's not possible to join only with physics and mathematics.
To Btech/BE you need to score minimum of 50% in qualifying examination with physics , chemistry and mathematics.
All the best.
See for getting admission in any of the engineering college u should be min. passed in the core subjects like CHEMISTRY , PHYSICS , MATHS. so if u are thinking to do btech with only two subjects u won't be getting that.
Hope u got my point. Ask if any query.