Question words

Question words, often called wh- words, are function words that can be used to ask open questions.

• We use what to ask for information about things and actions:

What do you want?

What’s she doing? Tell her to stop at once!

What time are you leaving?

• We use where to ask for information about place:

Where did you buy those shoes?

Where will you be working next Monday?

• We use when to ask for information about what time something happens:

When did you leave?

When are you going on holiday?

When will you know the result of the exam?

• How most commonly means “in what way” or “to what extent”. We often use how to introduce questions about measurements or amounts:

How old is your grandfather?

How often do you get to your cottage at weekends?

How much does the average DVD player cost these days?

How far is it to the Prado and how long will it take us to get there by taxi?

• We use who as an interrogative pronoun to begin questions about people:

Who’s next?

Who makes the decisions here?

Who did you talk to?

Whom is the object form of who. We use whom to refer to people in formal styles or in writing, when the person is the object of the verb. We don’t use it very often and we use it more commonly in writing than in speaking. We use whom commonly with prepositions. Some formal styles prefer to use a preposition before whom than to leave the preposition “hanging” at the end of the sentence.

• We use whose to ask a question about possession:

Whose birthday is it today?

Whose house was used in the film “Gosford Park”?

Whose are these gloves?

• We use why to ask about reasons and explanations:

Why did he leave home when he was 16?

Why didn’t you tell Gemma?

Why is the Earth round?

• We use which in questions as a determiner and interrogative pronoun to ask for specific information:

“Which car are we going in?” he asked Alexander.

Which museums did you visit?

Which do you prefer? Lemon cake or carrot cake?

• Which or what?

We use both which and what to ask questions. We use which when there is a restricted range of answers. We use what more commonly when the range of answers is not restricted:

Which is the capital of Liberia? Monrovia or Greenville?

What’s the capital of Liberia?

Source: https://dictionary.cambridge.org/ru/грамматика/британская-грамматика/question-words