You have the flexibility to offer both optional questions as well as required questions that the buyer will be required to answer before their purchase is completed. Requiring questions be answered is a powerful way to ensure that you have the data you need for each order and each participant.
It's important to remember that you should only require the questions you truly must have answered as requiring large amounts of questions degrades the user experience and can result in loss of revenue.
In order to require a question for an activity simply navigate to the product type you want to create or edit and either create a new product or edit an existing. On the Advanced Settings screen you will have a section for Questions. If you do not have the ability to select questions you will need to add at least one question.
Once at least one question is selected for your product you have the option to require the question be answered.
By checking the box in the above example we require that each participant answer what their name is if they are purchasing this item.