zāngyīfu zài zhèlǐ.

Because 在 is the key word for location here.

In Mandarin, to say that something is located somewhere, you usually use:

• A 在 B = A is at/in B

So:

• 脏衣服在这里。 = The dirty clothes are here.

是 is usually used to connect two nouns, as in:

• 他是老师。 = He is a teacher.

You normally do not use 是 just to say where something is.

Here, 在 expresses location: to be at / to be in.

A simple way to understand the sentence is:

• 脏衣服 = the dirty clothes
• 在 = are located
• 这里 = here

So the structure is:

• Subject + 在 + place

In more advanced grammar, 在 can sometimes be described differently depending on the sentence, but in this sentence it is easiest to treat it as the main location word: are here / are at this place.

Because this sentence is built as a basic location sentence:

• thing + 在 + place

So:

• 脏衣服在这里。 = The dirty clothes are here.

By contrast:

• 这里有脏衣服。 = There are dirty clothes here.

Both are natural, but they are not exactly the same in focus:

• 脏衣服在这里 focuses on where the dirty clothes are
• 这里有脏衣服 focuses on the existence of dirty clothes here

English often says Here are the dirty clothes, but Chinese usually keeps the thing first in a simple sentence like this.

Because 脏衣服 is a very natural noun phrase meaning dirty clothes or dirty laundry.

In Mandarin, short common modifiers often go directly before the noun without 的, especially in everyday combinations.

So:

• 脏衣服 = dirty clothes

You can also say:

• 脏的衣服

That is also correct, but it sounds a little more explicitly descriptive, like the clothes that are dirty.

A useful contrast:

• 脏衣服 = dirty clothes / dirty laundry
• 脏的衣服 = clothes that are dirty

In many everyday situations, 脏衣服 is the more natural choice.

They are doing different jobs.

• 脏衣服 = a noun phrase, dirty clothes
• 衣服脏 = a full statement, the clothes are dirty

So in your sentence:

• 脏衣服在这里。

脏 is part of the noun phrase 脏衣服.

But if you say:

• 衣服脏。

then 脏 is the predicate, meaning The clothes are dirty.

This is a very common difference in Chinese:

• adjective + noun → a noun phrase
• noun + adjective → a statement

A careful pronunciation is:

• zāng yīfu zài zhèlǐ

Tones:

• 脏 zāng — first tone
• 衣 yī — first tone
• 服 fu — usually neutral tone here
• 在 zài — fourth tone
• 这 zhè — fourth tone
• 里 lǐ — third tone

A couple of useful notes:

• 衣服 is usually pronounced yīfu, not yīfú
• In natural speech, 这里 may sound a little lighter, close to zhèli, though learners often start with zhèlǐ

Chinese nouns usually do not show singular vs. plural the way English does.

So 衣服 can mean:

• one item of clothing
• several clothes
• clothing in general

And 脏衣服 can mean:

• dirty clothes
• dirty clothing
• dirty laundry

The exact number depends on context. In many situations, English will translate it as dirty clothes or dirty laundry.

Yes, you can say:

• 脏衣服在这儿。

Both 这里 and 这儿 mean here.

General difference:

• 这里 — common and neutral
• 这儿 — more colloquial, especially in northern speech

So both are correct, and the choice is often just a matter of speaking style or regional preference.

No. Standard written Chinese normally does not put spaces between words.

So this would usually be written as:

• 脏衣服在这里。

Learning materials often add spaces to help beginners see the parts:

• 脏衣服 / 在 / 这里

But in normal Chinese text, it appears as one continuous line of characters.

No, not in normal Mandarin.

You need 在 to connect the thing and the place in this kind of sentence:

• 脏衣服在这里。 ✅
• 脏衣服这里。 ❌

Without 在, the sentence does not sound complete.

If you want a natural location sentence, keep the pattern:

• something + 在 + place