القطار في الموعد المحدد.

Because Arabic often uses a nominal sentence in the present tense, with no explicit verb for to be.

So:

• القطار = the train
• في الموعد المحدد = on time / at the specified time

Together, Arabic understands this as:

• The train is on time.

If you wanted was or will be, Arabic would usually add a verb such as كان or سيكون.

It is a nominal sentence made of:

• القطار — the topic / subject-like part
• في الموعد المحدد — a prepositional phrase giving information about it

A literal breakdown is:

• القطار = the train
• في = in / at
• الموعد = the appointment / scheduled time
• المحدد = specified / fixed

So the literal sense is something like:

• The train is at the specified time

which naturally becomes:

• The train is on time

في usually means in or at, but prepositions do not match perfectly across languages.

In this sentence, في الموعد المحدد is an idiomatic expression meaning:

• at the scheduled time
• on time

So even though English uses on, Arabic uses في.

This is very common: you should learn the whole phrase في الموعد المحدد as a set expression.

Because المحدد is an adjective describing الموعد, and in Arabic adjectives must agree with the noun they describe in definiteness.

Here:

• الموعد = the time / the appointment
• المحدد = the specified

Since the noun is definite, the adjective must also be definite:

• الموعد المحدد = the specified time

If the noun were indefinite, the adjective would also be indefinite.

Grammatically, المحدد is originally a passive participle from the verb حدّد meaning to specify / determine / set.

But in this sentence it functions like an adjective:

• الموعد المحدد = the specified / set / scheduled time

This is very common in Arabic: participles are often used as adjectives.

Because موعد usually refers to a set time, appointment, or scheduled time, not just time in a general sense.

Compare:

• وقت = time in a broad/general sense
• موعد = an appointed or scheduled time

So في الموعد المحدد emphasizes that the train is at its scheduled time, which is why it corresponds well to English on time.

In fully vocalized MSA, it would be:

• القطارُ في الموعدِ المحددِ

Why?

• القطارُ takes ḍamma because it is the opening noun of the nominal sentence
• الموعدِ takes kasra because it comes after the preposition في
• المحددِ also takes kasra because it is an adjective describing الموعد, so it matches it in case

In normal writing, these endings are usually omitted, but they are still understood grammatically.

Because of both position and meaning.

In Arabic, adjectives usually come after the noun they describe. Here:

• الموعد المحدد = the specified time

Also, the phrase begins with the preposition في, so في الموعد المحدد naturally forms one unit:

• in the specified time / at the scheduled time

It would not make much sense for المحدد to describe القطار here.

More or less, yes, if you translate word-for-word very literally. But that is not how you should understand it naturally.

A better way to think of it is:

• في الموعد المحدد = at the scheduled time

So the full sentence means:

• The train is on time
• The train is at the scheduled time

Literal translations can help you see the structure, but idiomatic meaning is more important.

Yes, that is possible, and it can also mean the train is on time.

Adding المحدد makes the phrase a bit more explicit:

• في الموعد = on time / at the appointed time
• في الموعد المحدد = at the specified/scheduled time

So the version with المحدد sounds slightly fuller or more formal.

It is pronounced roughly:

• al-qiṭār

The ق in قطار is a qāf, a deep q sound, not like English k. The ط is an emphatic ṭ.

Also, ق is a moon letter, so the ل in الـ is pronounced clearly:

• القطار = al-qiṭār

This is different from words beginning with a sun letter, where the ل assimilates.

It is perfectly understandable and natural in Modern Standard Arabic, especially in writing, announcements, or formal speech.

For example, it would fit well in contexts like:

• train schedules
• news reports
• station announcements
• formal descriptions

In everyday spoken dialects, people may use different wording, but in MSA this sentence is completely normal.

It helps to learn it in chunks rather than one word at a time:

• القطار = the train
• في الموعد = on time
• في الموعد المحدد = at the scheduled time / on time

A useful pattern to remember is:

• [noun] + في الموعد المحدد

For example:

• الطائرة في الموعد المحدد = The plane is on time
• الاجتماع في الموعد المحدد = The meeting is on time / at the scheduled time

This makes the structure easier to reuse.