What before a noun asks for general information when the answer is open. It points to a thing, idea, or person, but it does not limit the choice to a known group. In What book are you reading? the speaker asks for the name of any book. In What time does the train leave? what asks about a time, not about one choice from a list.

Use what when the noun is new information. It can describe common questions about objects, jobs, colors, reasons, and other facts: What color is your car? What job does she do? What size do you need? The noun stays after what, and the noun gives the question its topic.

Without the noun, what becomes an interrogative pronoun and asks for the whole answer by itself. Compare What book do you want? with What do you want? The first question needs a noun; the second does not.

Using what with general noun questions

Usage	Explanation
General information	Use what before a noun when you want general information and you are not choosing from a known set.
Open choice	Use what before a noun when the answer can come from many possibilities and there is no fixed group.
Unknown item	Use what before a noun when you do not know the name or type of thing you are asking about.

Which before a noun asks the listener to choose from a known set. The group is already clear in the situation, even if the speaker does not say every option. In Which jacket do you prefer? the jackets are part of a limited choice. In Which road leads to the station? the roads are specific roads in the area.

Use which when the answer comes from selection, not from open information. It often appears with things that can be compared side by side: Which day is better? Which city did you visit? Which flavor do you want? The noun remains after which, and the question asks the listener to identify one item from that group.

For meaning, which is narrower than what. What size do you need? asks for a size in general. Which size do you need? asks the listener to pick one size from the available sizes. That difference becomes clear in ordinary grammar, as in Demonstrative Adjectives and other adjective patterns.

Rules for which with known choices

Idea
Use which before a noun when you ask about a choice from a known group.
Make which match the noun that follows it in the question.
Use which when the speaker expects one answer from a limited set.

Whose before a noun asks who owns or controls something. It introduces the thing being asked about, while the owner is the unknown part of the question. In Whose phone is ringing? the question asks about the owner of the phone. In Whose keys are these? the speaker wants to know who the keys belong to.

The noun after whose can be singular or plural, and it follows normal noun grammar: Whose coat is on the chair? Whose shoes are by the door? The word whose does not change for number. It stays the same whether the noun is singular or plural.

Whose asks about possession, not about a quality of the noun. If the question needs an owner, whose comes before the noun. If the question needs the thing itself, the noun disappears and whose stands alone as an interrogative pronoun. Possessive forms also appear in Possessive Adjectives, where ownership is stated, not asked.

Using whose to ask about ownership

Usage	Explanation
Ownership of a thing	Use whose before a noun when you ask who owns something.
Relation to an item	Use whose before a noun when you want to know the person connected to that item.
Possessor focus	Use whose when the question focuses on the owner, not on the thing itself.

Interrogative adjectives come before the noun they describe. The pattern is what + noun, which + noun, or whose + noun. The noun follows immediately, as in What car did you buy? Which answer is correct? Whose bag is this?

In a question, the interrogative adjective usually begins the noun phrase, and the whole phrase comes near the front of the sentence. English questions often move the verb or auxiliary before the subject, but the interrogative adjective stays attached to its noun: What film did they watch? Which teacher called you? Whose idea was that? The noun does not move away from the interrogative word.

When a longer adjective phrase appears, it still belongs to the noun after the interrogative word. Compare What new phone did you get? with Which very old house did they sell? The interrogative adjective opens the noun phrase, and the noun remains the center of that phrase. For more word-building patterns, see Adjective Formation.

Word order for interrogative adjectives

Idea
Put the interrogative adjective before the noun it asks about.
Place the interrogative adjective near the front of the question.
Do not move the noun ahead of the interrogative adjective.

Interrogative adjectives need a noun after them. Interrogative pronouns do not. The difference is visible in the sentence structure. In What book are you reading? what is an adjective because it describes book. In What are you reading? what is a pronoun because no noun follows it.

The same contrast appears with which and whose. Which train is late? uses an adjective because train follows. Which is late? uses a pronoun because the noun is already understood or not needed. Whose coat is missing? contains an adjective. Whose is missing? contains a pronoun.

A good test is simple: if a noun comes after the word, the word works as an adjective. If the sentence ends the noun phrase there, the word works as a pronoun. That distinction is required for later study of Interrogative Pronouns.

Choosing adjective or pronoun form

Idea
Use an interrogative adjective when a noun follows it.
Use an interrogative pronoun when no noun follows it.
Check whether the question asks about a thing by itself or about a noun plus that thing.