Hello Shahid Aleem Raja!!!!
well, as far as subject selection of ur choice is concerned, u can opt for physics and any one math,whether pure maths or applied maths. The reason being that in css u have to chose optional subjects for 600 marks and from each group u can choose subjects of total 200 marks, not more than that. Now its upto u to choose two subjects with 100 marks each or one subject with 200 marks from one group.
Regards