How can I send radio button value in PHP using JavaScript?

ID has to be unique in a document −

var option_avail = $('input[name=option_avail]:checked', '#controls').val()
<label class="btn btn-primary active">
   <input type="radio" class="form-control" name="option_avail" value="Option_one" checked /> firstoption
</label>
<label class="btn btn-primary ">
   <input type="radio" class="form-control" name="option_avail" value="Option_two" /> secondoption
</label>
<label class="btn btn-primary ">
   <input type="radio" class="form-control" name="option_avail" value="Option_three" /> thirdoption
</label>