What Mode 1 squawk indicates intend bingo?

B indicates the correct squawk code for "intend bingo." The term "bingo" in aviation refers to a condition where an aircraft's fuel state is critically low, and the pilot must return to base or another suitable landing area. Each mode squawk code serves a specific purpose in communication and operational contexts.

In this case, squawk codes are used by air traffic control to identify and manage aircraft. A squawk of 71 is designated to alert controllers that a pilot intends to divert their flight due to low fuel, which is a crucial message for ensuring safety and efficient management of air traffic. The code allows air traffic controllers to prioritize that aircraft in their system, potentially providing it with a more direct route to safety or assistance.

The other options represent different modes or purposes that are not associated with indicating a low fuel state or "intend bingo," making them unsuitable for this particular context.