Комната абсолютно пустая.

In Russian, the present-tense verb to be is usually omitted in simple sentences like this.

So Russian says:

Комната абсолютно пустая

where English says:

The room is absolutely empty

This is called the zero copula. In the past or future, Russian does use a form of быть:

• Комната была абсолютно пустая — past
• Комната будет абсолютно пустая — future

Normally, no.

In modern Russian, есть is not the normal present-tense word for is in sentences like this. A neutral statement just leaves it out:

• Комната абсолютно пустая

The word есть more often means there is, exists, or adds special emphasis in certain contexts. So here, using есть would sound unnatural.

A very common pattern in Russian is:

• nouns ending in -а or -я in the nominative singular are usually feminine

Комната follows that pattern, so it is feminine.

You can also see that from the adjective that agrees with it:

• пустая is the feminine form

So the sentence itself confirms the gender.

Because adjectives in Russian must agree with the noun in gender, number, and case.

Here:

• комната = feminine, singular, nominative
• so the adjective must also be feminine, singular, nominative
• therefore: пустая

The dictionary form of the adjective is usually the masculine singular nominative, so you would normally look it up as пустой. But in this sentence it changes to пустая to match комната.

Комната is in the nominative singular, because it is the subject of the sentence.

Пустая is also nominative singular feminine, because it agrees with комната as the predicate adjective.

Абсолютно is an adverb, so it does not have case at all and does not change.

It is an adverb.

It modifies the adjective пустая, not the noun комната. In other words, it tells you how empty the room is:

• пустая = empty
• абсолютно пустая = absolutely empty

A lot of Russian adverbs end in -о, and unlike adjectives, they do not change to match gender, number, or case.

Yes.

• Комната пустая = the room is empty
• Комната абсолютно пустая = the room is absolutely empty

So абсолютно is just an intensifier. It makes the description stronger.

Yes, that is also correct.

Пуста is the short form of пустая. Russian adjectives sometimes have both:

• a full form: пустая
• a short form: пуста

Both can be used predicatively, but there is often a slight difference in feel:

• пустая sounds very common and everyday
• пуста can sound a bit more compact, literary, or state-focused

So both are good Russian, and you should recognize both.

Yes, Russian word order is more flexible than English word order.

The sentence as given,

• Комната абсолютно пустая

is a neutral way to say it.

But changing the order can change the emphasis. Also, some changes create a different structure:

• абсолютно пустая комната = an absolutely empty room
  This is now a noun phrase, not the same kind of full statement.
• Комната пустая = still a full sentence
• Пустая комната = usually just an empty room

So word order matters, even though Russian allows more flexibility than English.

The stress is:

• кОмната
• абсолЮтно
• пустАя

So the full sentence is:

кОмната абсолЮтно пустАя

A few helpful pronunciation notes:

• unstressed о is usually reduced, so it does not sound like a strong English o
• пустая has three syllables: пу-ста-я
• the stress in пустая is on -та-

Russian does not have articles like a, an, and the.

So комната can mean either a room or the room, depending on context.

In an actual conversation, context usually makes it clear. If the room has already been mentioned, English would often translate it as the room.

They are close in meaning, but the grammar is different.

• Комната абсолютно пустая directly describes the noun комната
• В комнате абсолютно пусто means something like In the room it is absolutely empty

In the second version, пусто is not an adjective agreeing with комната. It is a predicative word used to describe the situation in a place.

So:

• Комната абсолютно пустая = description of the room
• В комнате абсолютно пусто = description of what it is like in the room

Both can sound natural in English as The room is absolutely empty, but the Russian structure is different.