Hello student cut off vary every year on various factors like the level of question in the entrance examination and total number of applicants in that examination so its difficult to predict the exact marks but as per previous year records aim for marks around 600 so that you can get a admission into government medical college.

For more updates refer to the link mentioned below - https://www.google.com/amp/s/medicine.careers360.com/articles/neet-cutoff-tamil-nadu/amp

Feel free to comment if you have any doubt

Good luck