$query = $db->query("SELECT * FROM menu_link");
if ( $query->rowCount() ) {
$i=1;
foreach ($query as $row) {
if($i==4)
{
echo "<li class='class'><a href='#'>{$row['link_name']}</a></li>";
}else
{
echo "<li><a href='#'>{$row['link_name']}</a></li>";
}

$i++;
}
                        }