Which two instruments rely on the static vent?

The correct answer highlights the altimeter and vertical speed indicator as the instruments that rely on the static vent. Both of these instruments measure atmospheric pressure, which is essential for their operation.

The altimeter uses the static pressure to determine the aircraft's altitude. It does this by comparing the current atmospheric pressure with a predefined standard pressure, allowing the pilot to know how high they are flying above sea level or above a reference pressure level.

The vertical speed indicator (VSI) also depends on the static pressure readings. It detects changes in air pressure caused by the aircraft climbing or descending. As the aircraft ascends, the static pressure decreases, and the VSI reacts to these changes to indicate the rate at which the aircraft is gaining or losing altitude.

In contrast, the other options involve instruments that do not utilize the static pressure for their primary measurements. The turn coordinator and airspeed indicator use gyroscopic principles and dynamic pressure, respectively, while the attitude indicator, directional indicator, and turn coordinator rely on different sensors and mechanisms. The reference to nose wheel and main wheel does not pertain to flight instruments at all. This demonstrates the specific and crucial role of the static vent in providing accurate altitude and vertical speed readings in flight.