Thanks Chad for your help.
The options for the radio button are unique. The "None Chosen" option has the value of 0 and the other options have unique dollar values. I wanted the "None Chosen" option to be the default so the value of the radioButton would therefore be 0 and not null. I have chosen the "None Chosen" option as the default, but the form does not show any option selected when it is opened.
Screenshots are provided for the form view and the design view.