kiu

Kiu asks "who" or "which one" and also links a relative clause, so it covers English "who", "whom" and "which" in one word. It behaves like a noun or an adjective rather than a fixed particle: -n when it is the object (kiun vi vidis?) and -j in the plural (kiuj venis?), with both together in kiujn. Placed before a noun it means "which": kiu homo, kiun lingvon. It sits in the correlative table beside tiu ("that one"), ĉiu ("every one") and neniu ("nobody").