How to access this json data in JavaScript. when I alert it the result is undefined

Here is jQuery code

$.ajax({
    type: "POST",
    url: "frmMktHelpGridd.php",
    data: {
        labNo: secondElement
    },
    dataType: "json",
    beforeSend: function () {
        // Do something before sending request to server
    },
    error: function (jqXHR, textStatus, errorThrown) {
        alert('error has occured');
        alert(errorThrown);
    },
    success: function (data) {

        //Here is the problem

        alert(data[0]['Result']);
    }
});

This is PHP code

            $data=array($no);
    for($i=0;($i<$no && ($row=mysql_fetch_array($result)));$i++)
    {
        $data[$i]=array();
        $data[$i]['Result']         =   $row['Result'];
        $data[$i]['TestCode']       =   $row['TestCode'];
        $data[$i]['TestStatus']     =   $row['TestStatus'];
        $data[$i]['SrNo']           =   $row['SrNo'];
    }

    $data1=json_encode($data);

    echo $data1;
      exit;

I have tested the PHP file independently, The json data is output as follows:

      [{"Result":"1","TestCode":"22","TestStatus":"0","SrNo":"1"},{"Result":"1","TestCode":"23","TestStatus":"1","SrNo":"2"}]

$.ajax({
    type: "POST",
    url: "frmMktHelpGridd.php",
    data: {
        labNo: secondElement
    },
    dataType: "json",
    beforeSend: function () {
        // Do something before sending request to server
    },
    error: function (jqXHR, textStatus, errorThrown) {
        alert('error has occured');
        alert(errorThrown);
    },
    success: function (data) {
        //Added parse json
        var data = jQuery.parseJSON(data)

        alert(data[0]['Result']);
    }
});

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