<?php
$get_elements = array (
    'student_elements'     => 'firstname,lastname,mobileno,age,gender',
    'address_elements'     => 'building,sector,city',
    'marketing_elements'     => NULL,
    'office_use_elements'     => 'counsellername,mobile,email'
);

// Combine all strings
$get_elements = implode(',',$get_elements);

// DEBUGGING ONLY
echo $get_elements;

// Split the elements
$get_elements = explode(',', $get_elements);

// DEBUGGING ONLY
echo '<pre>'.var_export($get_elements, TRUE).'</pre>';

// YOUR CODE
foreach ($get_elements as $value) {
    // Ensure it's not empty
    if($value != ''){
        echo $sql_elements_get="SELECT fields_name, fields_type FROM `tbl_form_builder_fields` WHERE fields_name='".$value."'";
    }
}

?>

firstname,lastname,mobileno,age,gender,building,sector,city,,counsellername,mobile,email<pre>array (
  0 => 'firstname',
  1 => 'lastname',
  2 => 'mobileno',
  3 => 'age',
  4 => 'gender',
  5 => 'building',
  6 => 'sector',
  7 => 'city',
  8 => '',
  9 => 'counsellername',
  10 => 'mobile',
  11 => 'email',
)</pre>SELECT fields_name, fields_type FROM `tbl_form_builder_fields` WHERE fields_name='firstname'SELECT fields_name, fields_type FROM `tbl_form_builder_fields` WHERE fields_name='lastname'SELECT fields_name, fields_type FROM `tbl_form_builder_fields` WHERE fields_name='mobileno'SELECT fields_name, fields_type FROM `tbl_form_builder_fields` WHERE fields_name='age'SELECT fields_name, fields_type FROM `tbl_form_builder_fields` WHERE fields_name='gender'SELECT fields_name, fields_type FROM `tbl_form_builder_fields` WHERE fields_name='building'SELECT fields_name, fields_type FROM `tbl_form_builder_fields` WHERE fields_name='sector'SELECT fields_name, fields_type FROM `tbl_form_builder_fields` WHERE fields_name='city'SELECT fields_name, fields_type FROM `tbl_form_builder_fields` WHERE fields_name='counsellername'SELECT fields_name, fields_type FROM `tbl_form_builder_fields` WHERE fields_name='mobile'SELECT fields_name, fields_type FROM `tbl_form_builder_fields` WHERE fields_name='email'