Learn Spanish (Latin America): ¿Quién tiene la llave?

We use the singular quién when we assume one person has the key, or when we simply don't know. If we specifically expected multiple people to have it, we would use the plural form and ask ¿Quiénes tienen la llave?.

Why does quién use the tiene form of the verb?

When quién (who) is the subject of a question, Spanish treats it like a singular "he" or "she". That is why it takes tiene, which is the "he/she" form of the verb tener (to have).

Why does quién have an accent mark over the "e"?

In Spanish, all question words get an accent mark. Writing quién with an accent shows that it is being used to ask a question, which helps distinguish it from the word "quien" used in normal statements.

Could I use qué instead of quién if I don't know who has the key?

No, because qué means "what" and is only used to ask about things, ideas, or actions. Even if you don't know the answer, you are still asking for the identity of a person, so you must use quién (who).