JSFiddle - React, Tailwind, and code Playground

HTML

<script src="http://ajax.microsoft.com/ajax/jquery.validate/1.7/jquery.validate.js"></script>
<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8.2/themes/ui-lightness/jquery-ui.css">

 <select name="tur" id="tur">
        <option value="1">a</option> 
        <option value="2">a</option>  
        <option value="3">a</option> 
        <option value="4">a</option>
        <option value="5">b</option> 
        <option value="6">b</option>  
        <option value="7">c</option> 
         <option value="8">d</option>          
</select>

JavaScript

var array = [];

$('#tur option').each(function() {
    var $th = $(this);
    var text = $th.text();
    if( $.inArray(text, array) > -1 ) {
        $th.remove();
    } else {
        array.push( text );
    }
});