Learn Hardcore Croatian: Ovo je treći zadatak danas.

Without je, Ovo treći zadatak danas sounds ungrammatical in standard Croatian (except in very telegraphic styles like headings or notes). So you should keep je here.

Why is ovo neuter when zadatak is masculine?

This is one of the trickier points for English speakers.

ovo is a neuter demonstrative pronoun meaning “this (thing / situation here)”.
zadatak is a masculine noun.

In sentences like Ovo je treći zadatak, ovo acts as the subject, and treći zadatak is the predicate (what “this” is). Croatian allows the subject and the predicate to have different genders in such structures.

Compare:

Ovo je treći zadatak. – This is the third task. (neuter ovo
- masculine zadatak)
Ovaj zadatak je treći. – This task is the third. (masculine ovaj agreeing with zadatak)

So:

Use ovo when you say “This is X.” (pointing at something not yet named)
Use ovaj when you say “This X …” (and X is masculine: ovaj zadatak)

What case is zadatak in, and why doesn’t it change after je?

Zadatak is in the nominative singular:

zadatak – nominative singular (dictionary form)

After the verb biti (to be) in sentences like X is Y, the noun usually stays in the nominative, not accusative:

Ovo je treći zadatak. – both ovo and treći zadatak are in nominative.
Think of it as “This = the third task.” – both sides of the “equals” sign use nominative.

So you don’t say trećeg zadatka here; that would be a different function (e.g. genitive).

Why is there no word for “the” before treći zadatak?

Croatian does not have articles like “a/an” or “the”.

The phrase treći zadatak can mean:

the third task
a third task (in some contexts)

Definiteness (whether it’s “the” or “a”) is understood from context, word order, and sometimes intonation, not from a separate word.

In this particular sentence, given normal context in a lesson or exercise setting, Ovo je treći zadatak danas. is naturally understood as “This is the third task today.”

Why do we use treći and not tri here?

Croatian distinguishes:

cardinal numbers: jedan, dva, tri, četiri… (one, two, three, four…)
ordinal numbers: prvi, drugi, treći, četvrti… (first, second, third, fourth…)

In English you also say “third task”, not “three task”. Same in Croatian:

tri zadatka = three tasks (counting how many)
treći zadatak = the third task (position in an order)

Because you’re talking about the order (1st, 2nd, 3rd), you must use the ordinal: treći.

What form of treći is this, and how would it change with feminine or neuter nouns?

In Ovo je treći zadatak danas, treći is:

masculine, singular, nominative

It has to agree in gender, number, and case with zadatak (masculine singular nominative).

Basic nominative singular forms of “third”:

masculine: treći – treći zadatak (task – zadatak, masc.)
feminine: treća – treća vježba (exercise – vježba, fem.)
neuter: treće – treće pitanje (question – pitanje, neut.)

So if the noun changes, treći changes to match:

Ovo je treća vježba danas. – This is the third exercise today.
Ovo je treće pitanje danas. – This is the third question today.

Can danas go at the beginning of the sentence, and does that change the meaning?

Yes, you can move danas:

Ovo je treći zadatak danas.
Danas je ovo treći zadatak.

Both are grammatically correct.

The basic meaning (“This is the third task today”) stays the same, but word order affects emphasis slightly:

Ovo je treći zadatak danas. – neutral; focus is on “this is the third task”.
Danas je ovo treći zadatak. – puts more emphasis on today (“As for today, this is the third task”).

In ordinary speech, the original order (Ovo je treći zadatak danas) is more common and sounds more neutral.

Can I leave out je and say Ovo treći zadatak danas?

In normal, standard Croatian: no – you should not leave out je here.

Ovo je treći zadatak danas. – correct standard sentence.
Ovo treći zadatak danas. – sounds like a broken or telegraphic fragment.

Croatian can sometimes drop je in very informal, colloquial, or headline style, but that’s not something you should imitate as a learner, especially not in a simple, neutral sentence like this.

So: keep je.

How do you pronounce treći zadatak, especially the č?

Rough pronunciation (in English-like spelling):

treći ≈ TREH-chee
- tr as in tree
- e like in bed (but a bit more open)
- č like ch in church (a strong, hard “ch”)
- i like ee in see
zadatak ≈ zah-DAH-tahk
- z as in zoo
- each a like a in father
- t as in top
- k as in kite

Stress is usually:

TRÈ-ći ZA-DÀ-tak (main stress on the first syllable of treći, and on the second syllable of zadatak).
Exact accent patterns depend on dialect, but this will be well understood.

Is there a difference between Ovo je treći zadatak danas and Ovaj je treći zadatak danas?

Yes, there is a small difference.

Ovo je treći zadatak danas.
- ovo = “this (thing/situation here)”
- neutral, very common when you first identify what something is.
Ovaj je treći zadatak danas.
- ovaj = “this” (masculine, agreeing with zadatak)
- literally: “This one is the third task today.”
- Slightly more contrastive: you’re picking one specific task out of several and saying this one is the third.

In many contexts, both are possible, but Ovo je treći zadatak danas is the more neutral, typical way to introduce or point out the third task.

Could I reverse treći and zadatak and say zadatak treći?

You can say zadatak treći, but it sounds marked and is used in more formal, list-like, or stylistic contexts, for example:

in written instructions or math problems, as headings: Zadatak treći
in very formal or literary language for stylistic effect.

In everyday speech, when you’re just saying “the third task”, you should use:

treći zadatak – the third task

So for your sentence, stick with:

Ovo je treći zadatak danas. ✅
not
Ovo je zadatak treći danas. ❌ (sounds odd in normal speech)