Making a question required in a survey
Make a question required to ensure that your survey collects complete information.
In the header of Dev Studio, click.
Click the name of a survey, and then click the question that requires an answer.
In the Question settings section, select the Required check box.
This option is not available for multi-answer questions, however, you can make a multi-answer question required by performing validation on the answers that the user provides at run time.
Click Save survey.