Retain select option value in PHP

   <select class="form-control" id="oid">
         <option>--Select--</option>
        <?php
        while($row=mysqli_fetch_array($run))
        {
        ?>
        <option value="<?= $row['id'];?>"><?= $row['first_name'];?> #<?= $row['mobileno']; ?></option>
        <?php
        }
        ?>
   </select>




<?php
 echo $row['id'];

 ?>