Hello Deepika

Choose the field in which you have Keen interest.

If you want to prepare for UPSC then you will have to focus on those subjects from now only. Science stream and UPSC both are different fields .

UPSC , UNION PUBLIC SERVICE COMMISSION, is India' s premier central recruiting agency for public servants. It is responsible for appointments to and exam for All India services  and group A , group B posts under civil service cadre and defence service cadre if central government.

Science field is for Medical and Engineering professionals. To become a doctor or engineer you must have your maths ( for engineering ) and science ( specially biology for medical ) subjects. very strong.

You will have to appear for entrance exam for both streams. But the thing is what you really want, There is huge difference in x science and xii science.  Day today , competition in every field is getting tough.

As after x there will be a turning point for your career and future so think carefully, and start focusing on it. After all Dedication is required in all fields.