Final answer:
The Apple Watch uses its own unique operating system known as watchOS. It was created specifically for the smartwatch device, while other OS options from Apple are tailored to different devices.
Step-by-step explanation:
The operating system used by the Apple Watch, which was designed specifically for the device, is known as watchOS. Out of the given options, only watchOS is correct. iOS and OS X Mobile are other operating systems used by Apple but they are designed for iPhones and Macbooks, respectively. Tizen, on the other hand, is a Linux-based mobile operating system, but it is not associated with Apple; instead, it is used primarily by Samsung.
Learn more about watchOS