You can check internet is accessible or not when your device connected with WIFI with following code.
You need to import Reachability.h & Reachability .m in Appdelegate class and do following code in didFinishLaunchingWithOptions: function.

self.reachability = [Reachability reachabilityWithHostName:@”www.google.com”];
//self.reachability = [Reachability reachabilityForInternetConnection];

// Start Monitoring
[self.reachability startNotifier];

[[NSNotificationCenter defaultCenter] addObserver:self
selector:@selector(reachabilityChanged:)
name:kReachabilityChangedNotification
object:nil];

#pragma mark – Check Internet Network Reachability
-(void)reachabilityChanged:(NSNotification*)note
{

NetworkStatus remoteHostStatus = [self.reachability currentReachabilityStatus];

if (remoteHostStatus == NotReachable)
{
// Internet Connection not reachable
}
else if(remoteHostStatus == ReachableViaWiFi)  {
//Check Internet Connection Authenticated or Not when WIFI connected
[[[NSURLSession sharedSession] dataTaskWithURL:[NSURL URLWithString:@”http://google.com/”] completionHandler:^(NSData *data, NSURLResponse *response, NSError *error)
{
NSHTTPURLResponse *HTTPResponse = (NSHTTPURLResponse *)response;
NSDictionary *dict = [HTTPResponse allHeaderFields];
NSLog(@”%@”,dict);
NSString *strAccess = [dict valueForKey:@”Accept-Ranges”];

if ([strAccess isEqualToString:@”none”]) {
NSLog(@”Device is Not connected to the Internet”);
}
else{

NSLog(@”Device is connected to the Internet”);
UIViewController *VC = self.window.rootViewController;

UINavigationController* navVc = (UINavigationController*) VC;

for (UIViewController *objVC in [navVc viewControllers])
{
if ([objVC isKindOfClass:[PrivateChatVC class]])
{
[self.delegate updateSendButton:YES];
//[[NSNotificationCenter defaultCenter] postNotificationName:@”sendButtonEnable” object:nil];
break;

}
}

}
}] resume];

}
else if (remoteHostStatus == ReachableViaWWAN)  {
}
}