As krishna gopal said it differs to the teachers conecpts and different books. The solutions are given by teachers of Individual subjects and they are supposed to be master in their respective subjects. Generally students are coached by them so they follow what is taught to them. How to ensure that solutions given by various coaching Institute of repute to be correct as per IIT's perspective. Further you can not expect a 17 Years and 12 Graders to be a reasearch scholar in all the three subjects.

Is this a test of teachers of coaching institutes ot test of students. As per me only question which should have clear answers should be asked not the one where interpretation is possible.

Thanks Krishna Gopal. You have understood the pain of the student who had sleepless nights ( Owing to different answers for a few particular questions like the one in Chemistry part -1 where few institute declare a compound as only Optically active and other declares  that it has the same axis of symetry ) and wondering what went wrong.

Many many thanks for your understanding.