A passing threshold is the minimum number of questions a person needs to answer 'correctly' in order to Pass. If a person does not meet the passing threshold, their submission will be marked as Failed.
If your quiz does not have a passing threshold, the default result is always Unevaluated.
Adding a passing threshold
Go to Settings.
Click on Results and Feedback.
Enable the Pass or fail candidates switch, and enter the minimum number of correct answers required to pass.
Click on Save changes.