$sql="select * from question_test where test_id='".$test_id."' and difficulty_level BETWEEN ".$_SESSION['difficulty_start']." and ".$_SESSION['difficulty_end']." and question_id NOT IN ('".implode("', '", array_map('mysqli_real_escape_string', $_SESSION['question_attempt']))."') order by rand()*favourability_level desc";
On running the above code I get an error :
Warning: mysqli_real_escape_string() expects exactly 2 parameters, 1 given in C:\xampp\htdocs\exam.php on line 359