zhè shì dàrén de fángjiān.

的 is a very common particle used to link a modifier to a noun. Here it works a lot like English 's or of.

So:

• 大人 = adult / grown-up
• 房间 = room
• 大人的房间 = the adult's room / adults' room

A simple pattern is:

noun + 的 + noun

For example:

• 老师的书 = the teacher's book
• 我的朋友 = my friend
• 大人的房间 = the adult's room

Both can appear in Chinese, but 这是... is the most natural and standard way to say This is...

• 这 = this
• 这是... = this is...

这个 means this one or this + classifier, and it can also be used, but often adds a slightly different feel:

• 这是大人的房间。 = This is the adult's room.
• 这个是大人的房间。 = This one is the adult's room.

So in your sentence, 这 by itself is enough and sounds very natural.

是 is the verb to be in sentences that connect one noun to another noun.

Here the structure is:

这 + 是 + 大人的房间

Literally:

this + is + adult's room

So 是 links 这 and 大人的房间, just like is in English.

A useful basic pattern is:

A 是 B = A is B

Examples:

• 这是书。 = This is a book.
• 他是老师。 = He is a teacher.
• 这是大人的房间。 = This is the adult's room.

Even though the characters are:

• 大 = big
• 人 = person

the word 大人 is a fixed word meaning adult or grown-up in modern Chinese.

So you should learn it as one vocabulary item, not as a literal combination of big + person.

Also, depending on context, 大人 can sometimes have other meanings, such as an old-fashioned respectful title, but in a simple sentence like this, it usually just means adult or grown-up.

Chinese nouns often do not show singular/plural as clearly as English nouns do. So 大人的房间 can depend on context.

It may mean:

• the adult's room
• an adult's room
• adults' room

In real conversation, context usually makes it clear.

If you want to be more specific, you can add more words:

• 一个大人的房间 = an adult's room
• 那个大人的房间 = that adult's room
• 大人们的房间 = the adults' room

But in many cases, plain 大人的房间 is perfectly fine.

Because 这 here is standing on its own as this, not directly modifying a noun.

Compare:

1. 这是大人的房间。

   • 这 = this
   • 这是... = This is...

2. 这个房间是大人的。

   • 这个房间 = this room
   • Here you need the measure word 个 before 房间

So:

• 这 + 是... → no measure word needed
• 这 + measure word + noun → measure word is needed

Examples:

• 这是书。 = This is a book.
• 这本书很好。 = This book is very good.

It is pronounced dàrén:

• 大 = fourth tone (dà)
• 人 = second tone (rén)

So the tones go falling + rising.

Try saying it like this:

• dà — sharp falling tone
• rén — rising tone

And the whole sentence is:

Zhè shì dàrén de fángjiān.

Not exactly.

• 房间 = room
• 屋子 = room / house, depending on context
• 房子 = house / building

In your sentence, 房间 is the best word for room.

So:

• 大人的房间 = the adult's room

If you said 大人的房子, that would mean the adult's house, which is different.

Yes, grammatically you can, but the feeling is a bit different.

• 大人 = adult / grown-up in everyday language
• 成人 = adult, but often more formal or used in official/written contexts

So:

• 这是大人的房间。 = natural, everyday
• 这是成人的房间。 = more formal, less conversational

In daily speech, 大人 is usually more natural here.

Yes, it is grammatical and natural, especially if you are contrasting an adult's room with a child's room.

For example:

• 这是大人的房间，那是孩子的房间。 = This is the adult's room, and that is the child's room.

However, in real life, people are often more specific:

• 这是我爸妈的房间。 = This is my parents' room.
• 这是老师的房间。 = This is the teacher's room.

So your sentence is good Chinese, but the exact noun used would depend on the situation.

The basic order here should stay:

这 + 是 + 大人的房间

Chinese usually follows this pattern for identification:

this + is + noun phrase

If you change the order too much, it may become unnatural or mean something else.

For example:

• 这是大人的房间。 = This is the adult's room.
• 这个房间是大人的。 = This room belongs to the adult(s).

Both are correct, but they focus on slightly different things:

• 这是大人的房间 identifies what this is
• 这个房间是大人的 emphasizes who the room belongs to