What GPWS mode issues an aural indication of 'Glideslope'?

The choice indicating Mode 5 as the correct answer relates to the specific functionality of Ground Proximity Warning Systems (GPWS). Mode 5 is designed to monitor the aircraft's glideslope during an approach. When the aircraft deviates from the predetermined glideslope, Mode 5 provides an aural warning, which includes the indication of "Glideslope." This feature is critical for ensuring that pilots are made aware of any potential deviations from the ideal descent path, thereby enhancing safety during landing operations.

In contrast, other modes of the GPWS, such as Mode 2, Mode 4, and Mode 6, focus on different aspects of flight safety, such as terrain awareness or excessive descent rates, and do not specifically address glideslope issues or provide the same aural cues related to glidepath deviation. Mode 2 is generally associated with alerts for excessive descent rates, Mode 4 highlights terrain proximity, and Mode 6, which is around specific conditions in landings, does not include the glideslope alert either. Thus, Mode 5's specific emphasis on glideslope monitoring distinguishes it as the correct answer.