Learn Hardcore Croatian: Odgovor na pitanje je u knjizi. - The answer to the question is in the book.

Odgovor: nominative (the subject).
na pitanje: accusative (the preposition na takes the accusative in this “answer to” pattern).
u knjizi: locative (static location with u “in” uses the locative).

Why is it na pitanje (to the question) instead of something like o pitanju (about the question)?

Croatian uses the set pattern odgovor na + accusative to mean “answer to.”

odgovor na pitanje = answer to the question
Use o + locative to mean “about”:
rasprava o pitanju = discussion about the question/issue

Could I say odgovor pitanja to mean “the answer of the question”?

No. odgovor pitanja sounds wrong. Use odgovor na pitanje.
Genitive after odgovor is used for possession/agent, e.g. odgovor profesora “the professor’s answer.”

Why is it knjizi and not knjiga or knjigi?

You need the locative singular after u for static location: u knjizi.
The noun knjiga (book, fem.) forms the dative/locative singular as knjizi.
The change g → z before -i is a regular consonant alternation (k/g/h → c/z/s), e.g. noga → nozi, ruka → ruci.

Can I say u knjigu?

Only for motion into the book (accusative = movement). u knjigu means “into the book,” not “in the book.” Here you need the locative: u knjizi.

Where does je go in the sentence? Could it be first?

je is a clitic and normally goes in second position in the clause. It cannot be first.

Correct: Odgovor na pitanje je u knjizi.
Also correct (different focus): U knjizi je odgovor na pitanje.
Not as a statement: Je odgovor na pitanje…

Can I drop je?

Not in a normal statement. You need the verb: Odgovor na pitanje je u knjizi.
Negation is nije: Odgovor na pitanje nije u knjizi.
For emphasis, a full form jest is possible: Odgovor na pitanje jest u knjizi.

What are some natural word-order alternatives, and what do they emphasize?

Odgovor na pitanje je u knjizi. (neutral: new info is the location)
U knjizi je odgovor na pitanje. (emphasizes the place: “It’s in the book that…”)
Keep odgovor na pitanje together as a unit.

How do I make a yes/no question from this?

Use Je li… at the start:

Je li odgovor na pitanje u knjizi?
Colloquial: Da li je odgovor na pitanje u knjizi?

How do I ask “Where is the answer to the question?”

Gdje je odgovor na pitanje?
Short answer: U knjizi.

How do I say “The answers to the questions are in the books”?

Odgovori na pitanja su u knjigama.
Notes: odgovori (plural), pitanja (neuter plural), su (they are), knjigama (locative plural).

Why isn’t there any word for “the” in Croatian?

Croatian has no articles. Definiteness is understood from context or expressed with demonstratives if needed:

Taj odgovor na to pitanje je u ovoj knjizi. = That answer to that question is in this book.

Any quick pronunciation tips for the tricky parts?

odgovor: stress often on the first syllable; clear g as in “go.”
pitanje: nj = a single sound [ɲ], like Spanish ñ; je = “ye.”
knjizi: knj pronounced [kɲ]; j is like English y.
Trill the r lightly; all letters are pronounced.

When do I use u vs na for location?

u
- locative = inside/within: u knjizi, u kući.
na
- locative = on/at surfaces, institutions, events: na stolu (on the table), na fakultetu (at university), na koncertu (at a concert).

Is odgovor the same as rješenje?

Not quite.

odgovor = answer to a question.
rješenje = solution to a problem/task.
E.g. Odgovor na pitanje je u knjizi, but Rješenje zadatka je u knjizi.

How do adjectives agree here?

Adjectives match the noun they modify:

Masculine for odgovor: Točan odgovor na pitanje je…
Feminine locative for knjiga: …je u velikoj knjizi / u ovoj knjizi.