O negócio está aberto.

Because estar is normally used for a current state or condition, and open/closed is usually treated that way in Portuguese.

• O negócio está aberto. = The business is open.
• O negócio está fechado. = The business is closed.

Using ser here would sound different. É aberto usually describes a more permanent characteristic, not whether it is open right now.

For example:

• A porta está aberta. = The door is open.
• Ele é aberto a ideias novas. = He is open to new ideas.

So in your sentence, está is the natural choice.

Here, negócio means something like business, store, shop, or establishment, depending on context.

It is a flexible word in Portuguese. It can mean:

• a business/company
• a commercial establishment
• a deal
• a thing / that thing (in informal speech)

In O negócio está aberto, it most likely means:

• The business is open
• The shop is open
• The place is open

If you know exactly what kind of business it is, Brazilian Portuguese often uses a more specific noun:

• A loja está aberta. = The store is open.
• O restaurante está aberto. = The restaurant is open.

So negócio is understandable, but it is somewhat general.

Portuguese generally uses articles more often than English does.

So where English might say:

• Business is open
• The business is open

Portuguese strongly prefers:

• O negócio está aberto.

Without the article, Negócio está aberto, it sounds incomplete or unnatural in most normal situations.

The article o means the, and it tells us we are talking about a specific business.

Because negócio is a masculine noun.

In Portuguese, adjectives usually agree with the noun in gender and number:

• o negócio aberto → masculine singular
• a loja aberta → feminine singular
• os negócios abertos → masculine plural
• as lojas abertas → feminine plural

So:

• O negócio está aberto.
• A loja está aberta.

That final -o / -a changes to match the noun.

It functions like an adjective here.

Literally, aberto comes from the past participle of abrir (to open), but in sentences like this it works as a descriptive word meaning open.

So:

• está aberto = is open
• está fechado = is closed

This is not the same as saying has opened. It describes the current state of the business.

Not with the same meaning.

• O negócio está aberto. = The business is open.
  
  • This describes its current condition.
• O negócio abre. = The business opens.
  
  • This usually means it opens in general, or as part of a schedule/habit.

For example:

• O negócio abre às 9. = The business opens at 9.
• O negócio está aberto agora. = The business is open now.

So abre talks about the action or schedule; está aberto talks about the state.

Yes, it is grammatical and understandable, but whether it sounds fully natural depends on context.

Brazilian speakers often prefer a more specific word if they know what kind of place it is:

• A loja está aberta.
• O mercado está aberto.
• O restaurante está aberto.

O negócio está aberto can sound a little more general, like:

• the business is open
• the establishment is open
• the operation is open

It is fine, but not always the most common everyday wording if the speaker has a more specific noun available.

A rough pronunciation guide is:

oo neh-GOH-syoo es-TA ah-BEHR-too

A few notes:

• negócio has stress on gó: ne-GÓ-cio
• In Brazil, cio often sounds like syoo
• está has stress on the last syllable: es-TÁ
• aberto has stress on ber: a-BER-to

In natural speech, words connect smoothly, so está aberto may sound a bit like:

es-TAa-BER-too

Yes. Negócio is a very flexible word, and that can confuse learners.

It can mean:

• business
• deal
• thing / stuff / that thing in informal speech

Examples:

• Fiz um bom negócio. = I made a good deal.
• Que negócio é esse? = What is that thing? / What’s going on?
• Ele tem um negócio no centro. = He has a business downtown.

In your sentence, está aberto makes it clear we are probably talking about a business or establishment, because a deal is not normally described as open in this way.

Está is the third-person singular present indicative of estar.

So:

• eu estou = I am
• você/ele/ela está = you/he/she is
• o negócio está = the business is

In this sentence, it means is in the present:

• O negócio está aberto. = The business is open.

Very simply:

Negative:

• O negócio não está aberto. = The business is not open.

Question:

• O negócio está aberto? = Is the business open?

In spoken Portuguese, intonation often shows that it is a question. In writing, Brazilian Portuguese usually just uses the normal question mark at the end.

You can, but it is not the normal neutral order.

The standard order is:

• O negócio está aberto.

If you say:

• Está aberto o negócio.

it sounds marked, poetic, emphatic, or context-driven. It might appear in special situations, but it is not the default way a learner should say it.

So for normal everyday speech, use:

• O negócio está aberto.

Yes, very often in speech.

In informal Brazilian Portuguese, está is commonly shortened to tá:

• O negócio tá aberto.

This is extremely common in conversation, but in more formal writing you should use está.

So:

• está = standard / formal / written
• tá = informal / spoken

Both are widely understood.