Hello , 

There are 2 types of seat in tamilnadu

1. Pure govt seat (around 1lakh per annum)- 2650 seats
2. Govt seat in self financing clg( 8L pa) -800 seats

Minimum marks for the 1st,

General : 425–445 (31%)

BC: anything around 395(26.5%)

BCM: 350 above(3.5%)

MBC: 360 odd marks(20%)

SC/ST: above 300 maybe even less(19%)

Brackets indicate percentage of seat.

2nd:

Gen: abv 400

BC: 350+

BCM: abv 310

MBC: 315–325

SC/ST: 250 or less

Other than this there is private clg seats for which u need to pass there's not much competition so anything around 125 for general and around 100 for reserved will fetch u seat if u are ready to pay 25 lakhs pa.