I'm using Ajax, but the page is still refreshi

Question

This question already has an answer here:

• Pages Keeps Refreshing While Using AJAX 3 answers

I am trying to use this code. But Ajax doesn't work and the page is refreshing when I press the submit button. I don't know where is my mistake.

I'm using json because I need to print multiple answers. For instance, I need to show if each answer is correct.

I'm loading jQuery in the header, that is OK.

  <script>
$(document).ready(function() {
  $('form').submit(function(event) {
  var parametros = {
          "a" : a,
          "b" : b,
          "c" : c,
          "e" : d,
          "d" : e
  };
  $.ajax({
          data:  parametros,
          url:   'exercise_matching_code.php',
          dataType: 'json',
          type:  'post',
          beforeSend: function () {
                  $("#resultado").html("Procesando, espere por favor...");
          },
          success:  function (response) {
            $(".message1").html(data.message1);
            $(".message2").html(data.message2);
            $(".message3").html(data.message3);
            $(".message4").html(data.message4);
            $(".message5").html(data.message5);
          }
    });
  });
});
</script>
  <div class="row">
     <div class="large-12 columns">
     <p>Übung: Finde das Gegenteil:</p>
     <table style="width:100%">
      <tr>
        <td>a) schön</td>
        <td>1 alt</td> 
      </tr>
      <tr>
        <td>b) groß</td>
        <td>2 klein</td> 
      </tr>
      <tr>
        <td>c) neu</td>
        <td>3 langweilig</td> 
      </tr>
      <tr>
        <td>d) laut</td>
        <td>4 leise</td> 
      </tr>
      <tr>
        <td>e) interessant</td>
        <td>5 hässlich</td> 
      </tr>
     </table>
     </div>
  </div>
  <form action="" method="post">
    <div class="row">
       <div class="large-12 columns">
       <table style="width:100%">
      <tr>
        <td>a)</td>
        <td>
          <select name="a">
            <option value="1">1</option>
            <option value="2">2</option>
            <option value="3">3</option>
            <option value="4">4</option>
            <option value="5">5</option>
          </select>
          <div class="message1"></div>
        </td> 
      </tr>
      <tr>
        <td>b)</td>
        <td>
          <select name="b">
            <option value="1">1</option>
            <option value="2">2</option>
            <option value="3">3</option>
            <option value="4">4</option>
            <option value="5">5</option>
          </select>
          <div class="message2"></div>
        </td> 
      </tr>
      <tr>
        <td>c)</td>
        <td>
          <select name="c">
            <option value="1">1</option>
            <option value="2">2</option>
            <option value="3">3</option>
            <option value="4">4</option>
            <option value="5">5</option>
          </select>
          <div class="message3"></div>
        </td> 
      </tr>
      <tr>
        <td>d)</td>
        <td>
          <select name="d">
            <option value="1">1</option>
            <option value="2">2</option>
            <option value="3">3</option>
            <option value="4">4</option>
            <option value="5">5</option>
          </select>
          <div class="message4"></div>
        </td> 
      </tr>
      <tr>
        <td>e)</td>
        <td>
          <select name="e">
            <option value="1">1</option>
            <option value="2">2</option>
            <option value="3">3</option>
            <option value="4">4</option>
            <option value="5">5</option>
          </select>
          <div class="message5"></div>
        </td> 
      </tr>
      <tr>
     </table>
       </div>
    </div>
    <div class="row">
        <div class="large-12 columns submitting">
        <input type="submit" value="Go" class="submit">
        </div>
       </div>
  </form>

And this is the php file:-

<?php
$a = $_POST["a"];
$b = $_POST["b"];
$c = $_POST["c"];
$d = $_POST["d"];
$e = $_POST["e"];
if ($a == '2') {
    $answer1 = "correct answer";
    echo $answer1;
} else {
    $answer1 = "wrong answer";
    echo $answer1;
}
if ($b == '4') {
    $answer2 = "correct answer";
} else {
    $answer2 = "wrong answer";
}
if ($c == '1') {
    $answer3 = "correct answer";
} else {
    $answer3 = "wrong answer";
}
if ($b == '5') {
    $answer4 = "correct answer";
} else {
    $answer4 = "wrong answer";
}
if ($b == '3') {
    $answer5 = "correct answer";
} else {
    $answer5 = "wrong answer";
}
echo json_encode(
  array(
    "message1" => "$answer1", 
    "message2" => "$answer2",
    "message3" => "$answer3",
    "message4" => "$answer4",
    "message5" => "$answer5",
  )
) 
?>

Answer 1

You need to have the following piece of JavaScript to prevent the form from submitting.

$( 'form' ).on({
    submit: function() {
         return false;
    }
});

Answer 2

Use event.preventDefault() like below:-

$('form').submit(function(event) {
  event.preventDefault();

  //rest of the code

});

Reference:- https://api.jquery.com/event.preventdefault/