Hello,
If I consider previous years records, then a bc candidate must score 480-500 marks to be on safer side. Scoring 500 marks can increase possibility to get admission in any of the government medical colleges. 
Browse the link given below to check the college you can get on the basis of your marks-

http://www.medicine.careers360.com/articles/neet-cutoff-tamil-nadu
This is just a prediction based on previous year records. The result may vary this year.
Hope this helps,
Regards!

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