Picking between qué and cuál

Qué vs. Cuál

keh / KWAHL — What / which

"¿Qué es esto? vs. ¿Cuál prefieres, el rojo o el azul?"
What is this? vs. Which do you prefer, the red one or the blue one?

Rough rule: "qué" asks for a definition or open-ended answer, "cuál" asks to choose from a set of options. English uses "what" for both, which is exactly why this trips learners up.

"One of my favorite lessons to teach, because the confusion is so understandable and the fix is so satisfying."— Graciela