Die richtige Seitenzahl steht im Inhaltsverzeichnis.

Because Seitenzahl is a feminine noun in German: die Seitenzahl.

In this sentence, it is also the subject, so it is in the nominative case. That gives:

• die Seitenzahl = the page number

The adjective richtig has to match that structure, so after a definite article in the nominative feminine singular, it becomes:

• die richtige Seitenzahl

This is an adjective ending question.

In die richtige Seitenzahl, the adjective comes after the definite article die. With a definite article, the adjective takes a weaker ending. For feminine nominative singular, that ending is -e.

So:

• die richtige Seitenzahl
• die falsche Seitenzahl
• die genaue Seitenzahl

If the article changed, the adjective ending might change too.

It is in the nominative case because it is the subject of the sentence.

A good way to see that is to ask: What stands in the table of contents?
Answer: Die richtige Seitenzahl.

Also, the verb is steht, which is 3rd person singular, matching the singular subject die richtige Seitenzahl.

German often uses stehen literally for something that is written or printed somewhere.

So Die richtige Seitenzahl steht im Inhaltsverzeichnis means something like:

• The correct page number is listed in the table of contents
• literally, The correct page number stands in the table of contents

English usually says is in, appears in, or is listed in, but German often prefers steht in this kind of context.

For example:

• Das steht im Buch. = That is written in the book.
• Die Information steht auf der Website. = The information is on the website.

Yes, a native speaker would understand it, but steht is usually more natural when talking about information written in a text, document, list, or table.

So:

• ist im Inhaltsverzeichnis = understandable, but less idiomatic here
• steht im Inhaltsverzeichnis = the more natural choice

im is a contraction of:

• in dem → im

So:

• im Inhaltsverzeichnis = in the table of contents

German very often contracts in dem to im.

Other common contractions include:

• am = an dem
• zum = zu dem
• zur = zu der

Because this sentence describes a location, not movement.

German prepositions like in can take either:

• dative for location: where?
• accusative for direction/movement: where to?

Here the page number is located in the table of contents, so German uses the dative:

• im Inhaltsverzeichnis = in dem Inhaltsverzeichnis

Compare:

• Es steht im Inhaltsverzeichnis. = It is in the table of contents.
• Ich trage es in das Inhaltsverzeichnis ein. = I enter it into the table of contents.

It is in the dative singular because it follows in in a location meaning:

• in dem Inhaltsverzeichnis
• contracted: im Inhaltsverzeichnis

Inhaltsverzeichnis is a neuter noun:

• das Inhaltsverzeichnis

So the dative singular article is dem, which becomes im after in.

Most German nouns do not change in the singular dative. The article changes, but the noun often stays the same.

So:

• das Inhaltsverzeichnis = nominative
• dem Inhaltsverzeichnis = dative

The noun itself stays Inhaltsverzeichnis.

That is normal for many neuter nouns.

Seitenzahl is a compound noun:

• Seite = page
• Zahl = number

So Seitenzahl literally means page number.

This is very common in German: nouns are often joined together into one longer word.

It is another compound noun:

• Inhalt = content
• Verzeichnis = index, list, directory

So Inhaltsverzeichnis means table of contents.

It is a neuter noun:

• das Inhaltsverzeichnis

In German, all nouns are capitalized.

So in this sentence, these are capitalized because they are nouns:

• Seitenzahl
• Inhaltsverzeichnis

The adjective richtige is not capitalized because it is not being used as a noun here.

German main clauses normally follow the V2 rule: the finite verb comes in the second position.

Here the first element is the subject:

• Die richtige Seitenzahl | steht | im Inhaltsverzeichnis

That is the standard word order.

You could also move another element to the front, but then the verb still stays second:

• Im Inhaltsverzeichnis steht die richtige Seitenzahl.

That version is also correct.

The plural is:

• die Seitenzahlen

So:

• die richtige Seitenzahl = the correct page number
• die richtigen Seitenzahlen = the correct page numbers

Yes, absolutely.

Both are correct:

• Die richtige Seitenzahl steht im Inhaltsverzeichnis.
• Im Inhaltsverzeichnis steht die richtige Seitenzahl.

The difference is mainly focus:

• starting with Die richtige Seitenzahl puts more focus on the page number
• starting with Im Inhaltsverzeichnis puts more focus on where it is

In both sentences, the verb steht still stays in second position.