Question:

What determines the visibility of the system-generated "--None--" option on Radio or Picklist type survey questions in CRM?

Answer:

When a survey is viewed offline, there is no "--None--" option for the Radio question type, regardless of whether the question is required or not. However, if the question is not required and the user does not want to submit an answer to that question, they can leave it blank or deselect their answer by clicking on the selected radio button.

On Picklist question types, there is a "--None--" option available only if the question is not required. Required Picklist question types will not have a "--None--" option, as this ensures that users are capturing required information. 

When a survey is viewed online, the "--None--" option displays for both Picklist and Radio question types, regardless of whether the question is required or not. This is because, unlike offline behavior, once a selection is made it is unable to be deselected.

Although the "--None--" option displays on both question types online, it is only a valid answer for non-required questions. If the user answers "--None--" to any required questions, an error will prevent them from submitting the survey.

When the system-generated "--None--" option is selected, the value of the Response_vod__c field on the Question_Response_vod__c object will be an empty string (""). "--None--" will not be visible as an answer option while viewing data from the survey page and will therefore not be counted against the % Frequency.

The following table lays out the behavior of the "--None--" option for Radio and Picklist survey questions in Online/Offline and Required/Not Required scenarios:

Related Documentation:

CRM Help Documentation: Creating Survey Questions