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Unlike the Checkbox which allows select/unselect option because it also allows multiple selected option -- you cannot do this in Radio option button.
Because the Radio Option button allows only one selected option at a time, you cannot select/unselect a selected option.
If you want to clear a selected option in the Radio option you will need to reset/refresh the browser itself or add a Reset button on the form.
But please take note of the consequence of refreshing the browser or using the Reset button -- it will also clear all answers and data currently in the form.
Another option you may want to use is to set to ON the 'Allow Other' option of the Radio option button.
This will allow response outside the specified selection options.
Hope this help. Let us know if you need more assistance.