Which of the following is not classified as Controlled Airspace?

Class G airspace is classified as uncontrolled airspace, making it the correct answer to the question. Unlike controlled airspace, which requires the pilots to receive clearance from air traffic control and adhere to established regulations, Class G airspace operates under more flexible rules. In Class G airspace, pilots are not required to communicate with air traffic control and can operate under visual flight rules (VFR) without the need for a specific clearance, provided they comply with the basic visibility and cloud clearance requirements. This environment allows for a wider range of aircraft operations, particularly in areas where traffic is low.