Questions can be set to be required if a respondent answers a previous question, or set of questions, in a specific manner.
For example, if a respondent answers that they prefer Brand A over Brand B, you could make it mandatory for them to answer a follow-up question asking for more details.
When a question is set to be required, the respondent is forced to answer it before moving on to the next page or submitting the questionnaire.
First, you would begin with at least 2 questions; the first question determines if the second question would be shown or not. Make sure to add question identifiers! Next, set the second question as required. Then go to the Pages tab and click on Edit Survey Logic Rules. Make a new branch logic and fill in the if requirement. Example: “if question 1 equals choice 1″. Choose “Show a question” in the then statement and select the question you want to show for that requirement and voila.