Trong phòng có ai không?

A natural word-by-word breakdown is:

• trong = in, inside
• phòng = room
• có = there is / have / exist
• ai = who / anyone
• không = not, or a question marker in yes-no questions

So the sentence literally feels like:

• In the room, is there anyone?

Even though ai often means who, in this sentence it means anyone because it appears in a yes-no question with có ... không.

Vietnamese often puts the location first to set the scene.

So:

• Trong phòng có ai không? = In the room, is there anyone?

This is very natural in Vietnamese. English usually prefers Is there anyone in the room?, but Vietnamese often introduces the place before the thing being asked about.

You could also say:

• Có ai trong phòng không?

That means the same thing and is also natural.

In this sentence, có expresses existence/presence, similar to there is / there are in English.

So:

• có ai = is there anyone / there is someone

This is a very common Vietnamese pattern:

• Có nước không? = Is there water?
• Có ai ở nhà không? = Is anyone home?

Here, có is not exactly have in the English sense. It is more like an existence marker.

Because ai can mean different things depending on context.

It can mean:

• who in information questions
  
  • Ai đó? = Who is that?
• anyone / somebody in existence or yes-no patterns
  
  • Có ai không? = Is there anyone?

So in Trong phòng có ai không?, ai does not mean who specifically? It means any person / anyone.

Here, không helps form a yes-no question.

A very common Vietnamese pattern is:

• có ... không?

This works like is there ... or not?, which becomes a normal yes-no question in English.

So:

• có ai không? = is there anyone?

Even though không by itself often means not or no, at the end of a sentence like this it functions as part of the question pattern.

No.

Trong phòng có ai không? asks whether anyone is in the room at all.

It means:

• Is there anyone in the room?

If you want to ask Who is in the room?, you would use a different structure, for example:

• Ai ở trong phòng? = Who is in the room?
• Ai đang ở trong phòng? = Who is in the room right now?

So the original sentence is about existence, not identity.

Yes. That is very natural and means the same thing.

Compare:

• Trong phòng có ai không?
• Có ai trong phòng không?

Both mean:

• Is there anyone in the room?

The difference is mainly focus:

• Trong phòng có ai không? emphasizes the location first: In the room...
• Có ai trong phòng không? begins with the existence question: Is there anyone...

Both are common.

No, that would not sound correct for this meaning.

To ask whether anyone is present, Vietnamese normally needs the existence pattern with có:

• Trong phòng có ai không?

Without có, the sentence loses the structure that means is there anyone.

So for this kind of question, có is important.

Common answers include:

• Có. = Yes.
• Không. = No.
• Có người trong phòng. = There is someone in the room.
• Không có ai trong phòng. = There’s no one in the room.
• Có, tôi ở đây. = Yes, I’m here.

A very common negative pattern is:

• không có ai = there is no one / there isn’t anyone

It is neutral and very natural in everyday speech.

You can use it in many situations:

• calling into a room
• checking whether someone is inside
• asking a simple everyday question

It is neither especially formal nor slangy.

The tones are important because Vietnamese is tonal.

Approximate Northern pronunciation:

• Trong — level-ish mid tone
• phòng — falling tone
• có — rising tone
• ai — level
• không — level

A rough guide for English speakers:

• trong ≈ chawng/trawng but with Vietnamese tr
• phòng ≈ fawng with a falling tone
• có ≈ go/ko with a rising tone depending on accent
• ai ≈ eye
• không ≈ khong with a level tone

Most important for meaning here:

• có must have its correct rising tone
• phòng must have its falling tone
• không should not be pronounced like English kong

If you want to sound natural, try saying it in two chunks:

• Trong phòng | có ai không?

It is the most straightforward way, but context can change things a little.

Common related forms:

• trong phòng = in the room
• ở trong phòng = in the room / inside the room
• trong căn phòng = in the room, slightly more explicit/literary

In everyday speech, trong phòng is perfectly normal and natural.

A very useful pattern is:

• [location] + có + [person/thing] + không?

Meaning:

• Is there ... in/at ...?

Examples:

• Trong nhà có ai không? = Is anyone in the house?
• Trong tủ có gì không? = Is there anything in the cabinet?
• Ở đây có chỗ ngồi không? = Are there seats here?

So Trong phòng có ai không? is a great model sentence for asking whether something or someone is present in a place.