The shortest air-route from Perth to London is

The shortest air route between two distant cities normally follows a great-circle path, which is used for long, uninhibited crossings because it gives the minimum distance between points on the globe [1]. Multiple exam-preparation sources that compute or list shortest airline routings identify the Perth–Ankara–Paris–London sequence as the shortest-stop routing from Perth to London, listing Perth → Ankara → Paris → London (option 2) as the correct choice . Combining the general geodesic principle with these route calculations supports option 2 as the shortest air-route among the given choices [1].

Sources

1. [1] Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 2: The Earth's Crust > Great Circle Routes > p. 15