Your only problem is, that the dropdown is empty, isn't it?
To fill this dropdown: System > Configuration > Customers > Customer Configuration > Name and Address Options > Prefix Dropdown Options just fill in, whatever you want.
Protip:
If you want to have radio buttons instead, you have to array_filter() in your template, because there is an empty option added ;-)
Best Answer
You have to add field with require as bellow.
for example in my custom module the field i have added in
like
or as like bellow
I hope this will help you.