Q:

Know which Form is submitted

I have eight Forms in a page (Form0, Form1, Form2 and so on).  When a form is submitted, data is handed by JS and send to ReassignPreg.php, which search data in DB and send it back with json.  Then the proper divs on the page are updated. 
The code below is doing its job.  But I have eigh copies of almost the same code, one for each Form (I only copy two of them for brevity).  Newbie and amateur as I am, I wander which would be the way for synthesize this code (get Form name, and then pass that to only one function). 
<script type="text/javascript">
$(document).ready(function(){
  $("#Form0").submit(function(){
    var cadena = $(this).serialize();
    $.get('ReassignPreg.php?cadena='+cadena, function(row2){
      var text = row2;
      var obj = JSON.parse(text);
      var imagen='<img src="../ImageFolder/'+obj. File+'.png" width="530" />'

      $("#PregBox00").html(imagen)
      $("#PregBox01").html(obj. Clase)
      $("#PregBox02").html(obj. Dificultad)
      $("#PregBox03").html(obj. Tipo)
    });
  return false;
  });
});

$(document).ready(function(){
  $("#Form1").submit(function(){
    var cadena = $(this).serialize();
    $.get('ReassignPreg.php?cadena='+cadena, function(row2){
      var text = row2;
      var obj = JSON.parse(text);
      var imagen='<img src="../ImageFolder/'+obj. File+'.png" width="530" />'

      $("#PregBox10").html(imagen)
      $("#PregBox11").html(obj. Clase)
      $("#PregBox12").html(obj. Dificultad)
      $("#PregBox13").html(obj. Tipo)
    });
  return false;
  });
});
</script>

A:

A little more modularity helps a lot
$(document).ready(function () {
    $("[id^=Form]").on('submit', function (e) {
        e.preventDefault();

        var _form  = this.id.slice(-1); // 0, 1, etc
        var cadena = $(this).serialize() + '&form=' + _form;

        $.get('ReassignPreg.php?cadena=' + cadena, function (row) {
            var image = $('<img />', {
                src   : "../ImageFolder/" + row. File + ".png", 
                width : 530
            });

            $("#PregBox"+_form+"0").html(image);
            $("#PregBox"+_form+"1").html(row. Clase);
            $("#PregBox"+_form+"2").html(row. Dificultad);
            $("#PregBox"+_form+"3").html(row. Tipo);
        }, 'json');
    });
});

now you'll have a form key on the server containing the number of the form, for instance in PHP you'd get that with $_GET['form'] etc.