Požar može uništiti cijelu kuću.

Not exactly.

• požar = fire in the sense of a destructive fire, like a house fire, forest fire, blaze
• vatra = fire more generally, including a campfire, fireplace fire, flames, or fire as an element

So in Požar može uništiti cijelu kuću, požar is the natural choice because the sentence is about a damaging fire.

Because the subject is požar, which is third person singular.

The verb moći = to be able to / can
Its present-tense forms include:

• ja mogu = I can
• ti možeš = you can
• on/ona/ono može = he/she/it can

Since požar is singular and functions like it, Croatian uses može:

• Požar može... = A fire can... / The fire can...

Because after moći (can), Croatian normally uses an infinitive.

So:

• može uništiti = can destroy
• literally: is able to destroy

This works like English:

• A fire can destroy a whole house.

You do not conjugate the second verb here; only moći is conjugated.

Because uništiti is the infinitive, and it is also perfective.

A useful contrast is:

• uništiti = to destroy, to destroy completely, to bring to ruin
• uništavati = to be destroying, to destroy repeatedly or over time

In this sentence, the idea is a complete possible result: a fire can destroy the whole house. That makes uništiti very natural.

If you said Požar može uništavati kuću, it would sound more like:

• A fire can be destroying the house
• A fire can keep damaging the house

That is a different nuance.

Because kuću is in the accusative case.

The noun kuća is the direct object of uništiti:

• What can the fire destroy? → the whole house

In Croatian, direct objects often go into the accusative.

So:

• nominative: kuća = house
• accusative: kuću = house (as the object)

This is one of the most important patterns in Croatian grammar.

Because adjectives must match the noun they describe in:

• gender
• number
• case

Here, kuću is:

• feminine
• singular
• accusative

So cijeli (whole / entire) must also be feminine singular accusative:

• cijelu kuću = the whole house

Compare:

• cijela kuća = the whole house as subject
• vidim cijelu kuću = I see the whole house
• požar može uništiti cijelu kuću = a fire can destroy the whole house

Croatian has no articles like a/an/the.

So požar can mean:

• a fire
• the fire

The exact meaning depends on context.

Out of context, English would often translate this as:

• A fire can destroy a whole house.

But in a specific situation it could also mean:

• The fire can destroy the whole house.

The Croatian sentence itself does not force one of those choices.

It can correspond to several English versions depending on context:

• a whole house
• the whole house
• an entire house
• the entire house

The core meaning is that the house is destroyed completely, not just partly.

So cijelu kuću emphasizes totality.

Yes. Croatian word order is more flexible than English, although not completely free.

The neutral order here is:

• Požar može uništiti cijelu kuću.

You might also hear:

• Cijelu kuću požar može uništiti.
• Požar cijelu kuću može uništiti.

These alternatives usually change emphasis, not basic meaning.

For learners, the given version is the most natural and safest neutral order.

A rough pronunciation guide:

• požar ≈ POH-zhar

The letter ž sounds like the s in measure or the g in genre.

So:

• ž = a voiced zh sound

The stress is commonly on the first syllable: PÒžar.

A rough pronunciation is:

• kuću ≈ KOO-chyu, though English does not have an exact match

About ć:

• it is a soft consonant
• it is somewhat like ch, but softer and more palatal

And u is pronounced like oo in food.

So kuću sounds approximately like KOO-ću, with a soft ć sound.

In standard Croatian, the normal construction is:

• može uništiti

The pattern može da uništi is much more typical of Serbian and some neighboring varieties.

So if you are learning standard Croatian, you should prefer:

• Požar može uništiti cijelu kuću.

Yes, sometimes.

A common alternative is:

• čitavu kuću = the whole / entire house

So:

• Požar može uništiti cijelu kuću.
• Požar može uništiti čitavu kuću.

Both are natural.
cijelu is very common and neutral; čitavu is also common and often feels very close in meaning.

Požar is masculine singular.

Yes, that matters because it controls the verb form:

• požar može = fire can

If the subject were plural, the verb would change:

• požari mogu = fires can

In this sentence, however, požar is just the subject in nominative singular, so the form može is required.