https://www.realfastspanish.com/vocabulary/que-vs-cual

Qué vs Cuál – When to Use “What” and “Which” in Spanish
Spanish question words such as quién, cuándo, and dónde translate simply and smoothly between English and Spanish, not so for qué vs cuál.

Understandably, qué and cuál are challenging because their English equivalents ‘what’ and ‘which’ aren’t straightforward either.

Should you ask:

What book are you reading?

Or,

Which book are you reading?

Just like English, Spanish switches between these two questions words in not so obvious ways.

In this post, you’ll learn everything you need to know about qué vs cuál including how to ask questions about options and how to ask questions about definitions.

An overview of qué vs cuál
If you want to learn how to use qué and cuál properly in Spanish, you first need to stop thinking of these two Spanish questions words as the translation of ‘what?’ and ‘which?’.

You’ll likely end up going around in circles if you try to directly translate these English question words. And, you may even spend unnecessary time thinking about the correct use of ‘what?’ and ‘which?’ in English.

Instead, you’ll be much better off if you think of qué and cuál in phrase combinations with either a verb, noun, or preposition.

What this means is you now have more things memorise. But, the good news is there are only 6 phrases you need to know.

Moreover, any question that you could possibly want to ask in Spanish based around options or definitions could fit into one of these 6 question phrases.

The 6 phrases are:

¿Qué es…?
¿Cuál es…?
¿Cuál de…?
¿Qué (sustantivo)…?
¿Qué (verbo)…?
¿Cuál (verbo)…?

In the last few examples, ‘(verbo)’ represents a conjugated verb, and ‘(sustantivo)’ represents any Spanish noun you may want to use in your question.

Now, instead of translating ‘what?’ and ‘which?’, you simply need to choose between one of the above question phrases.

Note we see students in our Spanish classes making the most mistakes with the second and fourth constructions (I’ll explain why in the relevant sections below).

Let’s look at each question phrase in more detail.

Question phrase 1 – ¿Qué es…?
The first thing you should ask yourself: are you looking for the definition of a word or phrase?

If you are, you’ll need this first question phrase.

Think of ¿Qué es…? as asking “What is the definition of…?”.

For example:

English: What is (the definition of) a country?
Espanõl: ¿Qué es un país?

English: What is (the definition of) a family name?
Español: ¿Qué es un apellido?

English: What is (the definition of) a sentence?
Español: ¿Qué es una oración?

If you think the answer to your question would be in a dictionary then start your question with ¿Qué es…?

Question phrase 2 – ¿Cuál es…?
If your question isn’t related to the definition of an idea or concept but instead could have a variety of answers, you may need this second question phrase.

In fact, ¿Cuál es…? should be one of your go-to questions for asking about anything where more than one answer is possible.

Furthermore, you still need this construction even when it feels like there is only one answer such as asking someone’s name.

For example, this is not correct:

English: What is your name?
Español: ¿Qué es tu nombre? ⊗

If you want to ask someone’s name using a construction where you need to decide between qué vs cuál, you must use cuál.

English: What is your name?
Español: ¿Cuál es tu nombre?