What instrument provides information on the aircraft's vertical speed?

The instrument that provides information on the aircraft's vertical speed is indeed the rate of ascent or descent indicator, commonly known as the RA/VSI (Rate of Climb/Vertical Speed Indicator). This instrument is crucial for pilots as it displays the current vertical speed in feet per minute, indicating whether the aircraft is climbing or descending and at what rate.

The RA/VSI accomplishes this through the use of a static pressure system, which measures the change in air pressure as the aircraft moves up or down. A positive reading indicates a climb, while a negative reading shows a descent. This information is essential during ascent and descent phases of flight, helping pilots make informed decisions regarding altitude changes.

In comparison, the other instruments listed serve different purposes. The turn and slip inclinometer provides information regarding the aircraft's coordination during turns, not vertical speed. The EHSI (Electronic Horizontal Situation Indicator) primarily displays navigation information, such as course and heading, rather than vertical dynamics. The AOA (Angle of Attack) Indicator shows the angle between the wing and the oncoming air, which is more related to aerodynamic performance than vertical speed.