Which French Polynesian island group gives its name to UTC-09:30 time?

The Marquesas Islands give their name to UTC−09:30, the half-hour time offset used in that French Polynesian island group.

The Marquesas are a remote archipelago in the southeastern Pacific Ocean and form one of the administrative subdivisions of French Polynesia. Their local standard time is nine hours and thirty minutes behind Coordinated Universal Time, making the offset unusual among global time zones.

The group includes major islands such as Nuku Hiva and Hiva Oa. Unlike many regions that adjust clocks seasonally, the Marquesas use UTC−09:30 year-round. The principal settlement associated with the time zone is Taiohae, on Nuku Hiva.

The answer is not the Gambier Islands, Tuamotu Archipelago, or Society Islands. Those are separate French Polynesian island groups with different geographic identities and time arrangements. French Polynesia spans multiple time offsets because its islands are scattered across a vast area of the Pacific.