Learn Hardcore Dutch: Tom is een beetje jaloers op zijn zus, omdat zij al is geslaagd voor de toets. - Tom is a bit jealous of his sister, because she has already passed the test.

Tom is jaloers op zijn zus.
= Tom is jealous of his sister. (sounds stronger, more absolute)
Tom is een beetje jaloers op zijn zus.
= Tom is a bit / a little jealous of his sister. (softens it)

So een beetje makes the emotion sound weaker and more casual, similar to English kind of, a little, a bit.

Why is it zijn zus and not something like haar zus?

Zijn means his, and haar means her.

The possessive pronoun agrees with the owner, not with the noun that follows.
Here, the owner is Tom, who is male, so you must use zijn:

Tom is jaloers op zijn zus.
= Tom is jealous of his sister.

If the subject were a woman, you would use haar:

Anna is jaloers op haar zus.
= Anna is jealous of her sister.

The gender of zus (sister) does not influence the choice between zijn and haar; only the gender of the possessor does.

What is the difference between zij and ze, and why is zij used here?

Zij and ze both mean she (or they, in other contexts). The difference is formality and emphasis:

zij = stressed or more emphatic form
ze = unstressed, more neutral, more common in everyday speech

In the sentence:

Tom is een beetje jaloers op zijn zus, omdat zij al is geslaagd voor de toets.

Using zij slightly emphasizes she (his sister), contrasting her with Tom who has not passed yet. You could also say:

..., omdat ze al is geslaagd voor de toets.

This is also grammatically correct; it just sounds a bit less emphatic and more casual.

Why is the word order omdat zij al is geslaagd and not omdat zij is al geslaagd?

In Dutch subordinate clauses (clauses introduced by words like omdat, dat, als, wanneer, etc.), the conjugated verb moves to the end of the clause.

Structure of a subordinate clause:

[subordinator] + [subject] + (other stuff) + [verb(s)]

So:

omdat zij al is geslaagd
- omdat = because (subordinator)
- zij = she (subject)
- al = already (adverb)
- is geslaagd = has passed (auxiliary + participle, placed at the end)

Omdat zij is al geslaagd follows English word order and is incorrect in standard Dutch.

Why do we say is geslaagd instead of heeft geslaagd?

The verb is slagen (to pass), and in the expression slagen voor een toets/examen (to pass a test/exam), Dutch uses zijn (to be) as the auxiliary in the perfect tense:

slagen (voor iets) → perfect tense: zijn geslaagd (voor iets)
- Ik ben geslaagd voor de toets.
- Zij is geslaagd voor haar examen.

Using hebben here (heeft geslaagd) is ungrammatical in this meaning.

So:

zij is geslaagd voor de toets
= she has passed the test.

What does al mean here, and where can it appear in the sentence?

Al here means already.

zij al is geslaagd = she already has passed.

Placement: al is an adverb and usually comes before the verb cluster in a subordinate clause:

omdat zij al is geslaagd (most natural)
omdat zij is al geslaagd (wrong word order)

In a main clause, the position changes because of verb-second word order:

Zij is al geslaagd. (subject–verb–al–participle)
Al is zij geslaagd, hij is dat nog niet. (inversion for emphasis)

In your sentence, omdat zij al is geslaagd is the correct and natural position.

Why is there a comma before omdat? Is it mandatory?

In Dutch, it is normal and recommended (though not absolutely mandatory in all styles) to put a comma before a subordinate clause introduced by words like omdat, dat, als, etc., especially when the clause is longer.

Tom is een beetje jaloers op zijn zus, omdat zij al is geslaagd voor de toets.

The comma helps the reader see that a new clause is starting and reflects the natural pause in speech. In informal writing, you might see it omitted, but using the comma is good practice and very common.

What is the difference between omdat and want? Could we say ..., want zij is al geslaagd...?

Both omdat and want can be translated as because, but they behave differently:

Word order
- omdat introduces a subordinate clause → verb goes to the end:
  - ..., omdat zij al is geslaagd voor de toets.
- want introduces another main clause → normal main-clause word order (verb in second position):
  - ..., want zij is al geslaagd voor de toets.
Tone and usage
- omdat is slightly more neutral and is used very widely, both in speech and writing.
- want feels a bit more like giving an explanation or justification, and is frequent in spoken Dutch.

So yes, you can say:

Tom is een beetje jaloers op zijn zus, want zij is al geslaagd voor de toets.

Both are correct; they just use different clause types and word orders.

Why is it voor de toets? Do you always use voor after slagen?

With the meaning to pass (a test/exam), Dutch normally says:

slagen voor iets = to pass something (exam/test/course)

Examples:

Ik ben geslaagd voor het examen.
Zij is geslaagd voor haar rijbewijs.

So:

zij is geslaagd voor de toets
= she has passed the test.

Using another preposition like in here (geslaagd in de toets) would be wrong in standard Dutch. You can treat slagen voor (een toets/examen) as a fixed combination.

What exactly is a toets? How is it different from examen or test?

In Dutch educational context:

toets
- general word for test, quiz, exam paper
- often used for smaller or regular tests in school or university
examen
- more formal, often a final exam or larger, official exam
- e.g. eindexamen, rijexamen
test
- also exists in Dutch, borrowed from English
- used in many contexts (medical test, psychological test, technical test), sometimes interchangeable with toets, but toets is more “school-like”.

In your sentence, de toets suggests some kind of school or course test, not necessarily a big final exam.

Could we drop een beetje and just say Tom is jaloers op zijn zus? Would the meaning change?

Yes, you can say:

Tom is jaloers op zijn zus.

This is grammatically correct. The difference is in intensity:

Tom is jaloers op zijn zus.
= Tom is jealous of his sister. (sounds stronger, more direct)
Tom is een beetje jaloers op zijn zus.
= Tom is a bit jealous of his sister. (softer, more nuanced, maybe slightly embarrassed tone)

So een beetje reduces the strength of the statement and makes it sound more casual or polite.

Why is the verb at the end in ..., omdat zij al is geslaagd voor de toets? Is that a general rule?

Yes. In Dutch:

Main clause: the conjugated verb is in second position.
- Tom is een beetje jaloers op zijn zus.
  - is = 2nd element in the sentence
Subordinate clause (after omdat, dat, als, etc.): the verb (or verbs) go to the end.
- ..., omdat zij al is geslaagd voor de toets.
  - omdat = subordinator
  - zij al = subject + adverb
  - is geslaagd = verb cluster at the end

This verb-at-the-end order is a key feature of Dutch subordinate clauses.