Siódmy rozdział jest krótszy niż czwarty.

Polish does not have articles, so there is no separate word for the or a/an.

That means Siódmy rozdział can mean the seventh chapter or, depending on context, just seventh chapter. In normal use, the intended meaning is understood from the situation.

They are ordinal numbers: siódmy = seventh, czwarty = fourth.

In Polish, ordinal numbers behave like adjectives, so they change their form to match the noun they describe. Here they match rozdział.

• siódmy rozdział = seventh chapter
• czwarty rozdział = fourth chapter

Because they are all agreeing with rozdział, which is:

• masculine
• singular
• nominative

So the forms are:

• siódmy — masculine singular nominative
• krótszy — masculine singular nominative
• czwarty — masculine singular nominative

If the noun were feminine, the forms would be different, for example:

• siódma część jest krótsza niż czwarta

Because rozdział is a masculine inanimate noun in Polish. Nouns in Polish have grammatical gender, and that affects the form of adjectives, ordinal numbers, and some other words connected to them.

Since rozdział is masculine singular, the words describing it must also be masculine singular:

• siódmy rozdział
• krótszy
• czwarty

Jest is the 3rd person singular present form of być = to be.

Here it means is, and it is normally needed:

• Siódmy rozdział jest krótszy niż czwarty.

Leaving it out would sound incomplete in standard Polish. So unlike some headline-style or informal shortcuts, this normal full sentence keeps jest.

Krótszy is the comparative form of krótki = short.

So:

• krótki = short
• krótszy = shorter
• najkrótszy = shortest

This is a normal Polish comparative pattern: many adjectives form the comparative with endings like -szy or -iejszy, sometimes with a stem change.

So you should learn:

• krótki → krótszy

as a set.

Normally, no. For this adjective, Polish strongly prefers the simple comparative:

• krótszy = correct, natural
• bardziej krótki = unnatural in ordinary Polish

With many common adjectives, Polish uses a one-word comparative rather than bardziej + adjective.

Yes. After a comparative adjective like krótszy, niż means than.

So:

• krótszy niż czwarty = shorter than the fourth

This is one of the standard ways to make comparisons in Polish.

Yes. A very common alternative is:

• Siódmy rozdział jest krótszy od czwartego.

That also means the same thing.

The main grammar difference is:

• after niż, you often keep the form that fits the underlying sentence structure
• after od, you use the genitive

So compare:

• niż czwarty
• od czwartego

Both are correct here.

Because Polish, like English, often omits a repeated noun when it is obvious.

So:

• niż czwarty

really means:

• niż czwarty rozdział

English does the same:

• The seventh chapter is shorter than the fourth.

You do not need to repeat chapter, because the meaning is already clear.

Because the two comparison patterns work differently.

With niż, the phrase can be understood as a shortened version of a full comparison, something like:

• Siódmy rozdział jest krótszy niż czwarty rozdział jest.

That is why czwarty stays in the nominative here.

But od is a preposition, and od requires the genitive case:

• od czwartego
• od czwartego rozdziału

So:

• niż czwarty = nominative
• od czwartego = genitive

Yes, that is possible.

Both of these can occur:

• siódmy rozdział
• rozdział siódmy

But they do not feel exactly the same.

• siódmy rozdział is the more neutral everyday phrasing
• rozdział siódmy sounds more formal, label-like, or like a heading/title style

So in an ordinary sentence, Siódmy rozdział... is the most natural choice.

The given word order is the most neutral and natural one:

• Siódmy rozdział jest krótszy niż czwarty.

Polish word order is more flexible than English, but different orders usually add emphasis or sound stylistically marked. For a normal statement, the original order is the best one to learn first.

A rough pronunciation guide is:

• Siódmy ≈ SHOOD-mih
• rozdział ≈ ROZ-jaw
• jest ≈ yest
• krótszy ≈ KROOT-shih
• niż ≈ neesh
• czwarty ≈ CHFAR-tih

A few useful notes:

• ó sounds like u
• final ż in niż is pronounced like sh here
• Polish stress is usually on the next-to-last syllable, so in these two-syllable words it falls on the first syllable

These are only rough English approximations, but they are a good start.