zhège zhǐxiāng hěn zhòng.

In Mandarin, 这 (this) usually needs a measure word / classifier before a noun.

So:

• 这 = this
• 个 = a very common general classifier
• 纸箱 = cardboard box

That gives:

• 这个纸箱 = this cardboard box

English does not have this pattern, but Mandarin usually does. You normally cannot just say 这纸箱 in standard Mandarin.

Literally, 这个 is:

• 这 = this
• 个 = classifier

So it is closer to this one / this [classifier] in structure.

But in normal English translation, 这个纸箱 is simply this cardboard box.

Because in Mandarin, many adjectives can directly act as the predicate.

So instead of saying:

• This cardboard box is heavy

Mandarin says something closer to:

• This cardboard box very/heavy

In other words, 重 can function like is heavy by itself in the sentence. You do not use 是 before an adjective here.

So:

• 这个纸箱是重 ❌
• 这个纸箱很重 ✅

This is one of the most common questions learners have.

Although 很 often means very, in sentences like this it is often used just to make the sentence sound natural when an adjective is the predicate.

So:

• 这个纸箱很重 usually means This cardboard box is heavy
• It does not always mean This cardboard box is very heavy

If you strongly stress 很, then it can sound more like very:

• 这个纸箱很重。 = This cardboard box is heavy.
• 这个纸箱很重！ = This cardboard box is very heavy!

Yes, but it changes the feel.

• 这个纸箱很重 = neutral, natural statement
• 这个纸箱重 = more contrastive or emphatic, like This box is heavy (as opposed to something else)

Without 很, it can sound like you are making a comparison, contrast, or strong observation.

So for beginners, 很 + adjective is usually the safest pattern.

纸箱 means cardboard box or carton.

It is made of:

• 纸 = paper
• 箱 = box / chest / container

Together, 纸箱 refers to a box made of paperboard or cardboard.

In this sentence, 这个 is pronounced:

• zhège

A few helpful points:

• 这 is fourth tone: zhè
• 个 here is usually pronounced with a neutral tone, not a strong fourth tone

So it sounds like:

• zhè ge → written here as zhège

This neutral tone is very common in everyday speech.

Here, 重 is pronounced zhòng and means heavy.

This character has more than one pronunciation:

• zhòng = heavy, serious, important
• chóng = again, repeated, layered

In 很重, it must be zhòng because the meaning is heavy.

The word order is:

• 这个纸箱 = this cardboard box
• 很重 = is heavy

So the structure is:

• Subject + adjective predicate

More generally:

• Noun + 很 + adjective

Examples:

• 这个人很高。 = This person is tall.
• 那本书很贵。 = That book is expensive.
• 这个纸箱很重。 = This cardboard box is heavy.

You should learn 纸箱 as a normal vocabulary word meaning cardboard box, even though it is built from smaller parts:

• 纸 = paper
• 箱 = box

Knowing the parts helps you remember it, but in real use it functions as a single noun.

Yes. If you want to clearly emphasize very, you can say:

• 这个纸箱非常重。 = This cardboard box is very heavy.
• 这个纸箱特别重。 = This cardboard box is especially heavy.
• 这个纸箱真重。 = This cardboard box is really heavy.

These make the stronger meaning clearer than plain 很重.

You would usually say:

• 这个纸箱太重了。 = This cardboard box is too heavy.

Here:

• 太 = too
• 重 = heavy
• 了 adds a natural exclamatory or new-situation feeling

So 很重 is just heavy, while 太重了 is too heavy.

For this sentence, 个 is the normal, easy choice for learners.

• 这个纸箱 = this cardboard box

Mandarin classifiers can be tricky, and 个 is the most general and commonly used one. Even if some nouns may appear with more specific classifiers in other contexts, 这个纸箱 is a standard and natural phrase to learn and use.

Because that would mean something different.

• 这个纸箱很重。 = This cardboard box is heavy.
• 这个很重的纸箱 = this heavy cardboard box

The second one is a noun phrase, not a complete sentence by itself. It describes the box, but it does not finish the thought unless you add more:

• 这个很重的纸箱是谁的？ = Whose is this heavy cardboard box?

So your original sentence is a complete statement, while 这个很重的纸箱 is only a phrase.