bagaimana cara mengatasinya nya

iNotice: Undefined variable: mysql in C:\xampp\htdocs\pendaftaran\daftar.php on line 120

muncul eror

Warning: mysqli_query() expects at least 2 parameters, 1 given in C:\xampp\htdocs\pendaftaran\daftar.php on line 120

Warning: mysqli_fetch_row() expects parameter 1 to be mysqli_result, null given in C:\xampp\htdocs\pendaftaran\daftar.php on line 121

Notice: Trying to access array offset on value of type null in C:\xampp\htdocs\pendaftaran\daftar.php on line 123

include "config.php";
                    if($_GET['menu']=='daftar'){
                        $sql="SELECT * FROM pendaftaran WHERE menu='daftar'";
                        $content=mysqli_query($mysql);
                        $data=mysqli_fetch_row($content);

                        echo "$data[1]";
                        if($_POST['singlebutton']=="Daftar"){
                            $query="SELECT * FROM peserta_pendaftar WHERE nisn='$a'";
                            $content1=mysql_query($query);
                            $cek_nisn = mysql_num_rows($content1);
                            if($cek_nisn>0){
                                echo"
                                    <script type='text/javascript' language='javascript'>
                                        alert('NISN sudah terdaftar. Silahkan Login ke Menu Akun untuk Mengubah Data');
                                        window.location.href='daftar.php?menu=daftar';
                                    </script>";