Comparing database value with user input value

Question

I am creating a website which checks answers from user inputs and database values, here is my code,

<?php

$servername = "localhost";
$username = "root";
$password = "";
$dbname = "mydb";

// Create connection
$conn = new mysqli($servername, $username, $password, $dbname);
// Check connection
if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
} 

$sql = "SELECT * from questions";
$result = $conn->query($sql);  


$row = mysqli_fetch_array($result);
if($_POST['q1'] == $row['q1']){
    $send = mysql_query("insert into questions q1a values 'correct'");
    $result = mysql_fetch_array($conn,$send);
      die(mysql_error());

}else{
    echo "false";
}

?>

now i'm getting error saying,

Warning: mysql_fetch_array() expects parameter 1 to be resource, object given in C:\xampp\htdocs\pakaya\check.php on line 22 No database selected

how can i get rid of this error?

My database structure

qid | q1 | q1a | q2 | q2a