There is no certain number of attempts.

The maximum age is 25 years for general students .

So you can attempt neet only till 25 years .

There is further 5 more years relaxation given to OBC sc st students .

https://www.google.com/amp/s/medicine.careers360.com/articles/neet-eligibility-criteria/amp

Dear candidate, 

This is still.not clear from the bill which has been recently passed and would be clear later on but NEXT exam is final exam for the mbbs so it would take place once. 

If you don't get your desired branch,there might be an exam other than that which would take place.

As information comes,we would update it.

ALL THE BEST!