Môi trường sống không những sạch mà còn lớn.

It is a very common Vietnamese pattern meaning not only ... but also ....

So:

• không những sạch = not only clean
• mà còn lớn = but also large / big

This pattern links two qualities, actions, or facts and gives the second one extra emphasis.

Vietnamese often does not use a verb like to be before adjectives.

So instead of saying something like The living environment is clean, Vietnamese can simply say:

• Môi trường sống sạch
  = The living environment is clean

In your sentence, the same thing is happening, just inside the not only ... but also ... structure:

• Môi trường sống không những sạch mà còn lớn

So sạch and lớn are predicate adjectives.

Literally:

• môi trường = environment
• sống = to live / living

Together, môi trường sống means living environment, habitat, or the environment one lives in.

Here, sống tells you what kind of environment it is: one related to living.

In Vietnamese, modifier words often come after the main noun.

So:

• môi trường = environment
• môi trường sống = living environment

This is normal Vietnamese word order. English usually puts this kind of modifier before the noun, but Vietnamese often places it after.

Other similar patterns:

• nước uống = drinking water
• phòng ngủ = bedroom
• xe đạp = bicycle

The main thing comes first, and the describing word comes after.

• sạch = clean
• lớn = big, large

So the sentence says the living environment is not only clean but also large.

However, there is an important nuance: lớn usually describes physical size or scale. Depending on context, that may or may not sound natural with môi trường sống.

If the idea is spacious, Vietnamese often prefers words like:

• rộng = spacious, wide
• thoáng = airy, open
• thoải mái = comfortable

So lớn is understandable, but it may sound a little less natural than some alternatives.

It is grammatically correct, but môi trường sống ... lớn is a little unusual in many contexts.

Why?

Because môi trường sống is often somewhat abstract. People more naturally describe it with words like:

• sạch = clean
• tốt = good
• an toàn = safe
• trong lành = fresh / unpolluted

If you mean a place to live is physically spacious, a more natural sentence might be:

• Môi trường sống không những sạch mà còn rộng.

If you mean the habitat covers a large area, then lớn can make sense.

So the sentence is not wrong, but the best adjective depends on what kind of large you mean.

Yes. không những ... mà còn ... and không chỉ ... mà còn ... are very close in meaning.

So you could say:

• Môi trường sống không chỉ sạch mà còn lớn.

This is very natural too.

A rough difference:

• không những ... mà còn ... can sound a bit more formal or literary
• không chỉ ... mà còn ... is very common in everyday speech

Both are good to learn.

Yes, you usually can switch the two adjectives:

• Môi trường sống không những lớn mà còn sạch.

The basic meaning stays similar, but the emphasis changes slightly. The part after mà còn often feels a bit more highlighted.

So:

• không những sạch mà còn lớn puts a little more emphasis on lớn
• không những lớn mà còn sạch puts a little more emphasis on sạch

That said, naturalness still matters. If lớn feels odd with môi trường sống, switching the order will not fix that.

For learners, yes — it is best to use the full pair:

• không những ... mà còn ...

That is the standard structure.

Native speakers may sometimes shorten things in casual speech, but the full pattern is the clearest and safest choice. If you use không những, Vietnamese listeners usually expect a second part like mà còn.

No. Even though không often means not, in this pattern it is part of a fixed expression.

So không những ... mà còn ... does not mean a simple negative sentence. It functions as one unit meaning:

• not only ... but also ...

So the sentence is not saying the environment is not clean. It is saying the environment has two positive qualities.

A natural breakdown is:

• Môi trường sống / không những sạch / mà còn lớn

So:

1. Môi trường sống = the subject
2. không những sạch = first quality
3. mà còn lớn = second quality, with added emphasis

Thinking of the sentence in chunks like this makes it much easier to understand and produce similar sentences yourself.