Hello Dibyojyoti,

The basic statement of eligibility on the basis of 10+2 score for st Xavier's says that:

The minimum aggregate in 10+2 exam should be 60 percent. Those candidates belonging to the minority category should have 55 percent in their 10+2 examinations and those belonging to the reserve category should have 50 percent marks in their 10+2

So if you manage to score more than 60% aggregate in case of general then you are eligible for the test. 

All the best