If somebody has got just 52% marks in graduation, he/she is eligible for IIM's or not ?

Ya may be the he/ she will get a chance

Yes. he is eligible. It also depends on category and all.

The criteria changes every year. Last year it was around 50%. So yes you would be eligible but you would need high CAT percentile to be even considered for shortlisting and a very good reason for low marks in graduation during GD