The HTML code is as follows:

<select id="category" name="category">
<option value=""> Please select category </option>
<option value="1"> category 1</option>
<option value="2"> category 2</option>
<option value="3"> category 3</option>
<option value="4"> category 4</option>
</select>

Js code:

<script type="text/javascript">
$('#category option[value=3]').attr('selected',true);
</script>