Hey Harshita,

To clear you up on the choices you have for your subjects, I would put up the fronts:.   

1) Go with your interest. Studying whatever interests you more between the two.

2) Now talking about scope, I would personally favour Chemistry given the wide scope of Quantum studies, chemistry has to offer. The field of Quantum Computing is said to take over the science world and be the next big thing and it is widely covered in chemistry.

Best of luck with your decision.