De oorzaak leidt tot gevolgschade.

Because the subject is de oorzaak, which is third-person singular: the cause.

In the present tense, leiden changes like this:

• ik leid = I lead
• jij leidt = you lead
• hij/zij/het leidt = he/she/it leads
• de oorzaak leidt = the cause leads

So leidt is the correct singular present-tense form here.

Leiden tot is a very common Dutch combination meaning to lead to, to result in, or to cause.

So:

• iets leidt tot iets anders = something leads to something else

In your sentence:

• De oorzaak leidt tot gevolgschade.

the structure is:

• de oorzaak = the cause
• leidt tot = leads to / results in
• gevolgschade = consequential damage / resulting damage

It is best to learn leiden tot as a fixed pattern.

Because the verb leiden often takes the preposition tot when it means to lead to / result in.

Compare:

• Dit leidt tot problemen. = This leads to problems.
• De fout leidde tot vertraging. = The mistake led to delay.

So tot is not optional here if you want this meaning.
Without tot, leiden usually means something else, such as to guide:

• Ik leid de gasten naar binnen. = I lead the guests inside.

No. Leiden tot is not a separable verb.

That means you do not split it the way you would split a verb like opstaan.

For example:

• De oorzaak leidt tot schade.
• Het heeft tot schade geleid.

Notice that tot stays as a normal preposition, not as a separated prefix.

In Dutch, every singular noun is either a de-word or a het-word.

Oorzaak is a de-word, so:

• de oorzaak
• een oorzaak

Unfortunately, for many nouns you simply have to learn the article with the noun. A good habit is to memorize vocabulary as:

• de oorzaak = the cause

not just oorzaak by itself.

Because gevolgschade is being used in a general, uncountable sense here.

Dutch often leaves out the article with abstract or mass nouns after a preposition:

• tot schade leiden = lead to damage
• tot verwarring leiden = lead to confusion
• tot gevolgschade leiden = lead to consequential damage

If you mean a specific instance, an article is possible:

• De oorzaak leidde tot de gevolgschade. = The cause led to the consequential damage.

But in your sentence, the meaning is more general, so no article sounds natural.

Gevolgschade is a compound noun:

• gevolg = consequence/result
• schade = damage

Together, gevolgschade means something like damage that happens as a consequence of something else.

In Dutch, compound nouns are very common and are usually written as one word, so:

• gevolg schade ❌
• gevolgschade ✅

Also, the grammatical gender/article of a compound usually comes from the last part. Since schade is a de-word, gevolgschade is also a de-word.

Yes. This is normal Dutch main-clause word order:

• De oorzaak = subject
• leidt = finite verb
• tot gevolgschade = prepositional phrase

So it follows the usual pattern:

• Subject + finite verb + rest

Very literally:

• De oorzaak / leidt / tot gevolgschade
• The cause / leads / to consequential damage

Yes, often you can, but the nuance is a little different.

• leidt tot gevolgschade = leads to consequential damage / results in consequential damage
• veroorzaakt gevolgschade = causes consequential damage

Leidt tot can sound slightly more indirect or process-based: one thing results in another.
Veroorzaakt can sound more direct: it causes it.

In many contexts, both are acceptable.

This is a very common question.

• oorzaak = cause
• reden = reason

Oorzaak is used for a cause-effect relationship:

• De oorzaak van de brand = the cause of the fire

Reden is often used for an explanation, motive, or justification:

• De reden voor zijn vertrek = the reason for his departure

In your sentence, oorzaak is the right choice because the sentence is about one thing producing a result.

Leidt is pronounced roughly like English light, but with a Dutch l and t.

A rough guide:

• leidt ≈ lait

Important notes:

• The spelling ei in Dutch is usually pronounced like the vowel in English eye.
• The final dt is pronounced simply as t in normal speech.

So although it is written leidt, you hear something very close to lait.

Yes. In a subordinate clause, Dutch sends the verb to the end.

Main clause:

• De oorzaak leidt tot gevolgschade.

Subordinate clause:

• ... omdat de oorzaak tot gevolgschade leidt.
  = ... because the cause leads to consequential damage.

So the words stay the same, but leidt moves to the end of the clause, which is standard Dutch subordinate-clause word order.