Menonaktifkan item pertama di dropdownlist
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<select name="clientName" id="clientName">
<option name="" value="">Client Name</option>
<option name="Jennifer Black" value="0">Jennifer Black</option>
<option name="Henry Johnson" value="1">Henry Johnson</option>
<option name="Jack Hunnington" value="2">Jack Hunnington</option>
<option name="Mary Green" value="3">Mary Green</option>
</select>
$('option[value=""]').attr("disabled", "disabled");
Ram S