В комнате никого нет.

A very literal breakdown is:

• в = in
• комнате = room in the prepositional case, so in the room
• никого = no one / nobody in a non-nominative form
• нет = there is not / there isn’t

So the structure is roughly:

In the room, there is nobody.

That is why a natural English translation is There is nobody in the room or No one is in the room.

Because after в when it means in a place, Russian usually uses the prepositional case.

• dictionary form: комната = room
• prepositional singular: в комнате = in the room

This is a very common pattern:

• в доме = in the house
• в школе = in the school
• в комнате = in the room

So комнате is not a different word; it is the same noun in the case required by в for location.

Because нет requires the genitive case.

The pronoun никто means nobody / no one in the nominative form. But after нет, Russian normally uses genitive:

• nominative: никто
• genitive: никого

So:

• Никто здесь не работает. = Nobody works here.
• Здесь никого нет. = There is nobody here.

In your sentence, никого is used because the structure is about absence/existence: there is no one in the room.

Here it is best understood as genitive.

That is because нет governs the genitive case:

• нет времени = there is no time
• нет воды = there is no water
• нет людей = there are no people
• никого нет = there is no one

It is true that for animate words and pronouns, the genitive and accusative can look the same. But in this sentence, the reason for никого is specifically that нет takes genitive.

Because нет is the normal Russian word used to express absence in the present tense.

Compare:

• не = the general particle not
• нет = there isn’t / there is no / absent / no

Historically, нет comes from an old negative form related to есть, but for a learner the important point is this:

• To say that something does not exist / is not present, Russian usually uses нет.
• You normally do not say не есть in modern everyday Russian for this meaning.

So:

• В комнате никого нет = There is nobody in the room not
• В комнате никого не есть ❌

In Russian, the verb to be is usually omitted in the present tense.

So where English says:

• He is at home
• The book is on the table

Russian often just says:

• Он дома
• Книга на столе

However, in negative existential sentences like there is not..., Russian commonly uses нет.

So:

• affirmative: В комнате кто-то есть. = There is someone in the room.
• negative: В комнате никого нет. = There is nobody in the room.

This is why the sentence feels different from English: Russian often has no present-tense is, but it does use нет for absence.

Because Russian uses negative concord.

In standard English, two negatives are often taught as canceling each other out. Russian does not work that way. If you use a negative pronoun like никто, ничего, никогда, нигде, the verb is also normally negative.

Examples:

• Никто не знает. = Nobody knows.
• Я ничего не вижу. = I see nothing.
• Тут никого нет. = There is nobody here.

So никого нет is completely normal Russian. It does not mean a positive statement.

Yes, that is possible.

Both of these are natural:

• В комнате никого нет
• В комнате нет никого

The difference is mostly about emphasis and rhythm, not basic meaning.

Very roughly:

• В комнате никого нет sounds like a neutral statement: There’s nobody in the room.
• В комнате нет никого can put a little more focus on absence or sound slightly more emphatic in context.

Russian word order is more flexible than English, but not random. Different orders often reflect what is already known and what is new or emphasized.

Usually, no. That sounds unnatural in normal Russian.

Russian strongly prefers the existential pattern:

• В комнате никого нет

rather than a direct calque of English:

• Никто не в комнате ❌ or very unnatural

Why? Because Russian often expresses this idea as there is nobody in the room, not as nobody is in the room with в комнате attached to a negative form of to be.

So if you want to say No one is in the room, the idiomatic Russian sentence is still:

• В комнате никого нет

You replace нет with the appropriate past or future form of to be, while keeping the negative pattern.

• В комнате никого не было. = There was nobody in the room.
• В комнате никого не будет. = There will be nobody in the room.

Notice that in the past and future, Russian does not use нет. Instead it uses:

• не было = was not / there was not
• не будет = will not be / there will not be

But the overall structure stays the same: place + negative pronoun in genitive + negative verb.

Not with exactly the same meaning.

• В комнате никого нет = There is nobody in the room.
  This describes the current situation.

• В комнате никто не был = Nobody was in the room / Nobody has been in the room.
  This talks about whether anyone was there at some time, not about who is there now.

So even though the English translations may look related, the Russian grammar expresses different ideas:

• никого нет = absence now
• никто не был = no one was there / has been there

That distinction is very important in Russian.