In general, first to qualify in NEET, a General Category candidate has to score 50% of the top NEET score. It is 40% for SC, ST, OBC. For example, if the top NEET scorer has scored 500, General Category candidates should score atleast 250 and SC,ST,OBC should score around 200 to qualify. Now not every qualified candidate can get a medical seat. It depends on cut offs. Now cut offs change every year and are dependant on various factors like no.of seats available, no.of candidates appearing for the exam, difficulty of the exam and top NEET score. Every State except Jammu and Kashmir has All India Quota and State Quota and there is different cut off for each quota. Now every State has various cut offs for every college and Category. Tamilnadu is one of the States with highest cut off. But States like Assam do not have that high cut off. So it totally depends on what State you want to apply and if you want to apply under All India Quota or State Quota. State Quota has higher cut off marks. For Tamilnadu, it should be atleast 625. But for Himachal Pradesh it is around 300. And you cannot be eligible for State Quota of every State which means you should also try for All India Quota. But without having an idea of which State you want to apply for, it is difficult to guess your chances. For example, with the cut offs that Tamilnadu has, one can easily get a seat in a Govt. Medical college in West Bengal.

And 509 is a good score but not a guaranteed one for government seet....you may get it depends upon merit list

You can refer this link

https://medicine.careers360.com/articles/neet-college-predictor