text: Q:
  
  radio button selects list box change and pass null value to each list box
  
  when radio button selects  list box change and pass null value to each list box ...like Null value or empty space.....
  its java script code::
  <div>
      <input type="radio" name="rdo" id="rdo1" value="list1" />Radio1
      <select id="select1" style='display:none;'>
          <option value="l1">1.1</option>
          <option value="l2">2.2</option>
      </select>
  </div>
  <div>
      <input type="radio" name="rdo" id="rdo2" checked="checked" value="list2"/>Radio2
      <select id="select2">
          <option value="l1">2.1</option>
          <option value="l2">2.2</option>
      </select>
  </div>
  
  <script>
  function select1() {
      document.getElementById("select1").style.display="block";
      document.getElementById("select2").style.display="none";   
  }
  
  function select2() {
   document.getElementById("select2").style.display="block";
  document.getElementById("select1").style.display="none";             
  }    
  
  document.getElementById("rdo1").onclick = select1;
  document.getElementById("rdo2").onclick = select2;
  </script>
  
  A:
  
  I hope this what you expect.
  See in [jsFiddle][1]
  [1]: http://jsfiddle.net/x2n9W/1/. Now see my updated code
  function select1(someValue) {
          document.getElementById("select1").style.display = "block";
          var option = document.createElement("option");
          option.value = "";
          option.text = "";
          document.getElementById("select1").appendChild(option);
          document.getElementById("select2").style.display = "none";
  
      }
  
      function select2(someValue) {
          document.getElementById("select2").style.display = "block";
          document.getElementById("select1").style.display = "none";
          var option = document.createElement("option");
          option.value = "";
          option.text = "";
          document.getElementById("select2").appendChild(option);
      }
      document.getElementById("rdo1").onclick = function () {
          select1('someValue1');
      }
      document.getElementById("rdo2").onclick = function () {
          select2('someValue2');
      }
  
  