I need to know if SOAPUI sets default values for mandatory elements while sending request

Couple of things:

• That is because, if you want to test how the application is behaving if mandatory elements are missing
• However, you can check the request validation by right click and validate or Alt+v key combinations in the request editor
• If you want soapui to always check if the request is valid, then it can be done by using change of preferences. Check for Validate Requests in the documentation.