perfect code to validate at least one radio button is selected

function valbutton(form) {
// place any other field validations that you require here
// validate myradiobuttons
myOption = -1;
for (i=form.rbt_no.length-1; i>-1; i--) {
if (form.rbt_no[i].checked) {
myOption = i; i = -1;
}
}
if (myOption == -1) {
alert("You must select an option to proceed");
return false;
}
else
 
 
{
 
 
next_ques('next');
 
 
}
html:
onclick="<?php /*?>next_ques('next')<?php */?> valbutton(form);return false;"