Hello Davood. Depending on what you are trying to say, 1 and 3 are correct. The difference being that: I made a mistake is singular (one mistake). I made mistakes is plural (more than one mistake). Examples: The car is not running anymore, while fixing it, I made a mistake. I did not get my drivers license, because I made mistakes during the driving test. I hope this helps. Aleks

1- I made a mistake.