What occurs if no adjustments are made to the mixture control at higher flight altitudes?

At higher flight altitudes, the air becomes less dense, which directly affects the engine's ability to operate efficiently if no adjustments are made to the mixture control. When the density of air decreases, there is less oxygen available for combustion. If the mixture control is not adjusted, the amount of fuel flowing into the carburetor remains constant, which leads to a richer fuel-to-air ratio.

In such conditions, the engine may receive too much fuel relative to the amount of oxygen available, resulting in incomplete combustion. This can lead to reduced engine performance, rough running, or even potential engine failure if sustained. Therefore, without adjusting the mixture control to compensate for the decrease in air density at higher altitudes, the density of the air entering the carburetor does decrease while the fuel amount remains unchanged, confirming why the answer is correct.

Properly managing the mixture is essential for optimal engine performance during climbs to higher altitudes, highlighting the importance of this adjustment for flight safety and efficiency.