In short

Ukrainian uses one small set of pronouns to do two jobs. At the front of a question they ask about a person, a thing, or a quality: хто (who?), що (what?), яки́й (which? / what kind?). The very same words, placed between two clauses, become relative pronouns that hook a subordinate clause onto a noun or onto a whole idea: люди́на, яка́… (the person who…), усе, що… (everything that…). Learn the forms once and you have both functions for free — only the word’s role in the sentence changes, not its shape.

The rule

• хто points at people (and animals); що points at things, ideas and situations. They do not agree with anything — they only change by case (кого́, кому́, ким…).
• яки́й means which / what kind of. It declines exactly like a hard adjective and agrees in gender, number and case with the noun it describes: яки́й буди́нок, яка́ пі́сня, яке́ мі́сто, які́ лю́ди.
• As an interrogative, the pronoun opens the question and usually carries rising intonation: Хто це? Що це? Яки́й ко́лір?
• As a relative, the pronoun opens a subordinate clause and refers back to something in the main clause. It takes the case its own clause needs, not the case of the noun it points to: буди́нок (nom.), у яко́му (loc., because of у) я живу́.
• хто / що also head noun-clauses after verbs of knowing, saying, asking: Я не зна́ю, хто це. Скажи́, що ста́лося. Here they are still relative/connective, even without a preceding noun.
• In a relative clause, after a preposition you normally need the declinable яки́й (у яко́му, з яко́ю, про яки́й), because що, when it points back to a noun, does not itself take a preposition.

Forms & patterns

хто and що — no gender, no number, only case:

яки́й — declines like a hard adjective, agreeing in gender / number / case:

In the accusative, the second (genitive-like) form яко́го / яки́х is used when the noun is animate; яки́й / які́ when it is inanimate.

Examples

Common mistakes

• Хто твоя́ адре́са? -> Яка́ твоя́ адре́са? — хто asks about a person; for a thing or property use що / яки́й.
• Я зна́ю, яки́й прийшо́в. -> Я зна́ю, хто прийшо́в. — a person as the subject is хто, not яки́й.
• Як кни́га тобі́ подо́бається? -> Яка́ кни́га тобі́ подо́бається? — як = how; яки́й/яка́ = which and must agree with the noun.
• Яки́й пі́сня? -> Яка́ пі́сня? — яки́й agrees in gender: feminine пі́сня takes яка́.
• Дім, в що я живу́. -> Дім, в яко́му я живу́. — after a preposition use the declinable яки́й in the right case, not invariable що.
• з яки́й -> з яки́м — яки́й must decline; the instrumental after з is яки́м.

Tips

• Split the meanings cleanly: хто = who (people/animals), що = what (things/ideas), яки́й = which / what kind (a quality of a noun).
• Because яки́й declines like an adjective, decide its ending by asking which gender, which number, which case? — the same reflex you already use for до́брий, нови́й.
• A relative pronoun looks back at a noun but is dressed by its own clause: маши́на, яку́ я купи́в (яку́ = accusative object of купи́в), even though маши́на is nominative outside.
• Interrogative and relative are the same word doing different work: Хто це? (question) → Я не зна́ю, хто це. (linked clause). The form does not change.
• A preposition splits the two jobs: in a relative clause after a noun only яки́й takes it (у яко́му, з яко́ю, до яко́го, про яки́й); in a question хто and що take it freely (про що, з ким, до ко́го).
• Keep яки́й apart from як (how) and from котри́й (which one of a set); mixing them is a frequent slip.