I would go with 2, but would change "circle" to "circles".
Which of the following is correct?
1. Choose the best answer by blackening the circle for Question 1-4 and complete Question 5.
2. Choose the best answer by blackening the circle for Questions 1-4 and complete Question 5.
Thanks a lot!
I would use "filling in" the circle(s).
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.