Any degree or graduation/post-graduation in any subject is alright. For higher education, one should always pursue the subject which one finds interesting and is comfortable with. Academic career and interest should not be compromised for an uncertain and highly competitive career in civil service.
If you find physics or chemistry really exciting, please go for that. I always feel a good science student has greater flair and ability to write precise answers in a logical and objective manner.
First of all, if you think that you want to be an IAS then I will suggest you to go for Bachelor In Arts.
You can take majors Political science or sociology.
This subjects help one to crack any government exams like UPSC, SSC CGL and State Public Comission Exams and RRB too.
This subjects are very informative and easy to understand.