De zaal heeft dertig stoelen.

Because zaal is a de-word in Dutch. Dutch nouns take either de or het in the singular, and zaal belongs to the de group.

So:

• de zaal = the hall / the room

There is no simple universal rule that lets you always predict de or het, so this often has to be learned with the noun.

A useful extra point:

• plural nouns always take de
• so de stoelen is automatic because it is plural

Zaal usually means a fairly large room, hall, or auditorium-like space. The exact English translation depends on context.

It can refer to:

• a hall
• a room
• a venue space
• sometimes a ward or salon in certain contexts

So in this sentence, zaal suggests something like a hall or room with chairs in it.

That is a very natural question. Dutch often uses hebben (to have) in places where English prefers there is / there are.

So:

• De zaal heeft dertig stoelen. literally = The hall has thirty chairs.
• natural English meaning = There are thirty chairs in the hall.

Dutch can also express this idea in a way closer to English:

• Er staan dertig stoelen in de zaal.

That sentence literally means There stand thirty chairs in the hall, but idiomatically it means There are thirty chairs in the hall.

So both patterns exist in Dutch:

• X heeft Y = X has Y
• Er staan / zitten / liggen ... = there are ..., with the verb chosen partly by how the object is positioned

Because the subject is de zaal, which is singular.

The verb hebben is conjugated like this in the present tense:

• ik heb
• jij/u hebt
• hij/zij/het heeft
• wij hebben
• jullie hebben
• zij hebben

Since de zaal is a singular third-person subject, Dutch uses heeft.

In a basic Dutch main clause, the usual word order is:

subject + finite verb + rest

So in:

• De zaal heeft dertig stoelen

the parts are:

• De zaal = subject
• heeft = finite verb
• dertig stoelen = object

A simple test is to ask: who or what has thirty chairs?
Answer: de zaal

That makes de zaal the subject.

The singular is stoel = chair.
The plural is stoelen = chairs.

This is a very common Dutch plural pattern:

• singular noun + -en

So:

• stoel → stoelen

Other nouns form plurals differently, but -en is one of the most common endings.

Because dertig stoelen is the direct object of heeft.

The structure is simply:

• de zaal = the hall
• heeft = has
• dertig stoelen = thirty chairs

No preposition is needed, just as in English:

• The hall has thirty chairs

If Dutch wanted to express location more explicitly, it might use a different structure:

• Er staan dertig stoelen in de zaal.

There, in de zaal is the location phrase.

Because Dutch numbers normally do not change form before nouns.

So:

• dertig stoelen = thirty chairs
• dertig boeken = thirty books
• dertig tafels = thirty tables

Unlike adjectives, numbers like dertig do not get an extra ending here.

Grammatically, yes, but it means something different.

• De zaal heeft dertig stoelen. = a specific hall/room has thirty chairs
• Een zaal heeft dertig stoelen. = a hall has thirty chairs / one hall has thirty chairs

Using de points to a specific hall already known from context.
Using een makes it indefinite, so it sounds more general or introduces it as new information.

In many contexts, een zaal heeft dertig stoelen would sound a bit odd unless you are describing one hall among others, or giving an example.

Yes. Dutch main clauses follow the verb-second rule, which means the finite verb usually stays in the second position.

So besides:

• De zaal heeft dertig stoelen.

you could also say:

• Vandaag heeft de zaal dertig stoelen.
• In dit gebouw heeft de zaal dertig stoelen.

Notice what happens:

• the first element changes
• the verb heeft still stays in second position
• the subject moves after the verb if something else comes first

So Dutch is not just subject-verb-object all the time; the finite verb wants to be in position 2 in main clauses.

In a subordinate clause, the finite verb typically moves to the end.

For example:

• Ik zie dat de zaal dertig stoelen heeft.
• We weten dat de zaal dertig stoelen heeft.

Compare:

• main clause: De zaal heeft dertig stoelen.
• subordinate clause: ... dat de zaal dertig stoelen heeft.

This is one of the biggest word-order differences between Dutch and English.

A rough learner-friendly pronunciation is:

• de ≈ duh
• zaal ≈ zahl
• heeft ≈ hayft
• dertig ≈ DAIR-tikh or DER-tikh
• stoelen ≈ STOO-luh(n)

A few notes:

• aa in zaal is a long vowel
• ee in heeft is also a long vowel
• the g in dertig is the Dutch throaty sound in many accents
• the oe in stoelen sounds like oo in food

A more IPA-like version is approximately:

• də zaːl heːft dɛrtəx stuːlə(n)

It is natural Dutch, especially if the focus is on what the hall contains or has available.

But depending on context, a native speaker might also say:

• Er staan dertig stoelen in de zaal.

That version focuses more on what is physically present in the room.

Very roughly:

• De zaal heeft dertig stoelen. = the hall has thirty chairs available / as part of its setup
• Er staan dertig stoelen in de zaal. = there are thirty chairs standing in the hall

Both are correct; the best choice depends on nuance and context.