When is the stall speed of an airplane highest for a given configuration?

The stall speed of an airplane is influenced by several factors, including the aircraft's weight and its center of gravity position. Stall speed increases with weight; thus, a higher gross mass leads to a higher stall speed due to the increased aerodynamic load on the wings.

When the aircraft carries maximum allowable mass, the lift generated must counterbalance this additional weight. If, in this scenario, the center of gravity is positioned forward, the aircraft tends to have a higher angle of attack before stalling, which means that the stall speed reaches its peak. A forward center of gravity can make the aircraft less stable, requiring a higher angle of attack to maintain level flight. This increased angle of attack results in a higher stall speed when the plane is at its maximum allowable weight, as the aerodynamic characteristics push the stall to occur at greater speeds.

Thus, the combination of maximum allowable mass and a forward center of gravity maximizes the stall speed, making it the correct choice.