Hey Deepak,

St. Xavier college Kolkata  will choose students for the UG programme based on their academic performance and an interview.

For BSc Mathematics or physics the qualifying criteria is

• Candidates that have passed the 12th grade with a PCM stream. A minimum of 60% on the qualifying exam is required.
• The college will publish a merit list based on the results of the most recent exam.
• Candidates who have been shortlisted will be eligible for a college interview.
• On the college's official website, the final merit list of selected candidates will be posted.

With your percentage there is a chance that you will get there, but I would personally suggest you should refer different colleges as well because there cut-off also goes high as per the number of applicants.

Best of luck.

Regards.