Which of these are true?
1. If you pick an apple and let it go, it falls.
2. If you pick an apple and let go of it, it falls.
3. If you pick an apple and let go of, it falls.
1 and 2 are correct. (They also happen to be true, but your question is about grammatical correctness.)
Rolex_Cellini, please state that you are not a teacher, in accordance with the first of the Notices above.