how do i add radio button in custom field.
You would need to find a developer to write a customfield plugin to do that. I had a quick look at https://moodle.org/plugins/?q=type:customfield , but no one seems to have published such a plugin type yet.
It would be very similar to the 'dropdown menu' type (customfield_select), with only the form output being different. At a guess, an experienced Moodle developer could put something like that together with a few hours work.
It would be very similar to the 'dropdown menu' type (customfield_select), with only the form output being different. At a guess, an experienced Moodle developer could put something like that together with a few hours work.