how to change checkbox unchecked in jquery code example

Example 1: jquery set checkbox checked unchecked

//jQuery 1.6+ use
$('.checkbox').prop('checked', true);  //false for uncheck
//jQuery 1.5.x and below use
$('.checkbox').attr('checked', true);  //false for uncheck

Example 2: get unchecked checkbox jquery

if ($("#check_box_id").is(':checked')) {
  alert("checked");
}else{
  alert("unchecked");
}