Class JSONSerialization = NSClassFromString(@"NSJSONSerialization");

if (JSONSerialization) {
    NSLog(@"NSJSONSerialization exist!");
}
else
{
    NSLog(@"NSJSONSerialization not exist!");
}

JSONSerialization = NSClassFromString(@"JSONSerialization");

if (JSONSerialization) {
    NSLog(@"JSONSerialization exist!");
}
else
{
    NSLog(@"JSONSerialization not exist!");
}