Before installing an antivirus software on your device, you must understand how does an antivirus work. An antivirus will monitor apps which have been installed by you and prevents them from modifying the core files of the operating system. This is the basic function of antivirus on a smartphone. For this, the antivirus also needs to hook itself up to the core files. Other additional features such as find my iPhone, geo-location, password manager, secure web browsing etc can be obtained by non-antivirus apps as well.
Coming to iOS, Apple's iOS (iPhone, iPod, and iPad) has designed in such a way that the operating system is strongly fenced from the apps. This method is called as sandboxing. Unless your device is jailbroken, there is no way that any third party app can dwell into or modify the core files of the operating system. The architecture is so strong that you don't need any antivirus program for an iOS device and this is the reason that Apple has removed many antivirus apps from the App store since 2015. Since iOS is sandboxed and an app cannot access core files, the antivirus itself cannot function because it is too restricted (an antivirus needs access to core files to work). So in other words, an antivirus app on iOS is useless and you need not install any special programme to prevent your device from being hacked.
The antivirus programs which are available in App store generally provide same features as I have mentioned above and those features can be obtained by other apps which are not antivirus programs. Also, those other apps will provide more enhanced features (such as password manager, Anti-theft etc) than the antivirus itself.
Dr. V. Shashikanth