In ServiceNow, the Application Picker is a tool that allows developers to select the active application scope. When an application is selected from the Application Picker, it sets the Application Scope to that application. This means that any configurations, scripts, or customizations made will be associated with the selected application's scope. Therefore, the correct answer is D.
The other options are incorrect:
A . Selecting Global in the Application Picker sets the Application Scope to Incident: Selecting "Global" sets the scope to the global application, not specifically to Incident.
B . Global is a reserved application which does not appear in the Application Picker: The Global application does appear in the Application Picker and can be selected.
C . Selecting an application from the Application Picker does not set the Application Scope: Selecting an application does set the Application Scope.
For more detailed information, refer to the official ServiceNow documentation on Application Scope.