Una pieza completa de código PHP agradable y claro que devuelve JSON
$option = $_GET['option'];
if ( $option == 1 ) {
$data = [ 'a', 'b', 'c' ];
// will encode to JSON array: ["a","b","c"]
// accessed as example in JavaScript like: result[1] (returns "b")
} else {
$data = [ 'name' => 'God', 'age' => -1 ];
// will encode to JSON object: {"name":"God","age":-1}
// accessed as example in JavaScript like: result.name or result['name'] (returns "God")
}
header('Content-type: application/json');
echo json_encode( $data );
Weary Weevil