Urrrrrrrrrrrgent please

I have a page with Dynamic view of input radio buttons for a poll
as follows:

<input name=selecta type=radio dir=rtl lang=ar value="from Database" id="first" >
<input name=selecta type=radio dir=rtl lang=ar value="from Database" id="second" >
<input name=selecta type=radio dir=rtl lang=ar value="from Database" id="third" >


and it depends on the poll Quiz . some of them have 2 radio answers and other have 3 or 4 ...etc . Now I need to make validation for those button so No one can click the button untill he/she chooses one of the button (I know how to do the vaildation) but I need a Javascript code (if statement) to check by the ID of the tag object if it's available or not inside the page that what I need .......
can some one give me the code pleeeeeeeeeeeeeez?


Best Regards
Devilware