Learn Hardcore Croatian: Ona je žedna poslije posla, pa uzima sok iz hladnjaka. - She is thirsty after work, so she takes juice from the fridge.

Because the adjective agrees with the subject in gender and number. Ona (she) is feminine singular, so the predicate adjective is žedna (feminine). For comparison:

On je žedan (masc.)
Dijete je žedno (neuter)
Oni su žedni (masc. plural)
One su žedne (fem. plural) Predicate adjectives are in the nominative.

What is the role of je in Ona je žedna, and why is it placed there?

Je is the present tense of biti (to be). It’s a clitic and prefers the second position in its clause. Ona je žedna is the neutral order. If you front something, je still tends to sit in second position: Poslije posla je žedna.

Why is it poslije posla and not poslije posao?

The preposition poslije (“after”) requires the genitive case. Posao (work/job) in the genitive singular is posla. So: poslije posla = “after work.”

Can I use nakon instead of poslije? What about posle?

Yes, nakon also takes the genitive and is fully standard in Croatian: nakon posla. Posle is common/standard in Serbian; Croatian standard prefers poslije.

What does pa mean here, and why is there a comma before it?

Pa is a coordinating conjunction meaning roughly “so/and then,” showing a mild consequence or sequence. When pa connects two independent clauses, Croatian normally uses a comma before it: …, pa ….

Why uzima and not uzme? What about uzeti?

Uzima is the imperfective present of uzimati and describes an action in progress or a habitual action (“she takes/is taking”).
Uzme is the perfective present of uzeti; perfective present typically points to the future or appears in certain subordinate/narrative uses, not for “right now” descriptions.
For a single completed past action, use perfective past: Uzela je sok (“She took the juice”).
For future: Uzet će sok (“She will take the juice”).

Why choose uzima (“takes”) instead of pije/popije (“drinks”)?

The sentence focuses on getting the juice from the fridge, not on drinking it. If you want “drinks,” use:

pije sok = is drinking/drinks (imperfective, process)
popije sok = drinks it up/finishes it (perfective, completed action)

Why is it sok (not soka) as the object?

Sok is a masculine inanimate noun. In the singular, the accusative equals the nominative: vidim sok. You’ll see soka (genitive) in partitive-like expressions: pije malo soka (“drinks a little juice”).

Why iz hladnjaka and not od hladnjaka or s/sa hladnjaka?

iz
- genitive = “out of/from inside” something: iz hladnjaka (from the fridge’s interior).
od
- genitive = “from (a person/source/origin)” or distances/causes, not used for “out of a container.”
s/sa
- genitive/ablative-like use = “off/from the surface of” (e.g., sa stola = off the table), not appropriate for a container’s interior.

Is hladnjak the usual word for “fridge”? Any alternatives?

Yes, hladnjak is standard in Croatia. Frižider (a loanword) is also very common and fully understood: iz frižidera. Don’t confuse with ledenjak (glacier).

Can I drop ona?

Yes. Croatian often omits subject pronouns when context is clear: Žedna je poslije posla, pa uzima sok iz hladnjaka. The verb/adjective endings and context show the subject.

Can I move parts of the sentence around?

Yes, word order is flexible for emphasis, but keep clitics in second position. Examples:

Poslije posla je žedna, pa uzima sok iz hladnjaka.
Ona je poslije posla žedna, pa iz hladnjaka uzima sok.
Iz hladnjaka uzima sok (focus on the source). All are grammatical; the choice affects what is emphasized.

How would I refer to “the juice” with a pronoun to avoid repeating it?

Use the masculine object clitic ga (for sok): Ona je žedna…, pa ga uzima iz hladnjaka. Place ga in the clitic slot (second position in its clause).

Any pronunciation tips for žedna and hladnjak?

ž = the “s” in “measure” (voiced “zh”).
nj in hladnjak = a palatal sound like “ny” in “canyon.” So roughly [HLAD-nyak].