Hello Vishnu, 

B.Sc Chemistry is a merit based subject. For admission in this course you require passing your 10+2 with subjects such as biology, physics and of course chemistry, seperately in both theory and practicals. 

The eligibility criteria for he course is around Atleast 75% for most colleges. But the cut-offs differ according to the college you are talking about so it is better to select a few colleges and look through their eligibility criteria before deciding on a college. 

I hope this helped.