- array_diff: documentation ( source)
- json_encode: documentation ( source)
<?php
$arr_database = array("V1", "V2", "V5", "V6", "V7", "V10");
$arr_custom = array("V1", "V2", "V3", "V4", "V5", "V6", "V7", "V8", "V9", "V10");
$arr_output = array_diff($arr_custom, $arr_database);
echo json_encode($arr_output);