grammar.pronouns.interrogative
Question words: qué, cuál, quién, cuánto
Qué asks for definitions or things; cuál picks from a set; quién(es) asks about people; cuánto/a/os/as asks quantity. All carry accents in questions.
grammarA1, A2✓ Reviewedv0.1.0
Explanation
The interrogatives are qué, cuál(es), quién(es), cuánto/a/os/as, plus dónde, cuándo, cómo, por qué. They all carry a written accent in questions — direct and indirect — which is what separates them from the unaccented relatives and conjunctions (qué vs que, quién vs quien): no sé qué hacer keeps its accent.
Qué asks for a definition or identification and is the choice directly before a noun: ¿qué es esto?, ¿qué libro querés? Cuál asks you to choose from a set, and is standard before ser when you're not defining: ¿cuál es tu número? (saying *¿qué es tu número? would ask for a philosophical definition).
Quién and cuánto agree: quiénes for several people (¿quiénes vienen?), cuánta/cuántos for quantity in gender and number (¿cuántas personas?, ¿cuánto cuesta?). These same words introduce exclamations, again with the accent: ¡qué calor!, ¡cuánta gente!
Examples
What's your email?
Region: global
Who (all) is going on the trip?
Region: global
How many of us are there, and who's missing?