Need Help

[eluser]phpfresher[/eluser]
I need the following output:
<select name = "XXX" id="XXX" class="xxx">
<option value="">XXX</option>
<option value="">XXX</option>
</select>
Here is my code:
&lt;?php
$js = 'id="module_id"';
echo form_dropdown('module_id',$list_of_module,$js);
?&gt;
And this code outputs only :
<select name = "module_id" >
<option value="">XXX</option>
<option value="">XXX</option>
</select>

How can i insert id into select box or drop down box need help