Bruksenhetsnummeret står på døren.

Because Norwegian usually writes compound nouns as a single word.

Here, bruksenhetsnummeret is built from:

• bruksenhetsnummer = the dwelling-unit number / unit number
• -et = the definite ending, giving the ... number

This is very normal in Norwegian. Where English often uses several words, Norwegian often combines them:

• togstasjon = train station
• mobilnummer = mobile number
• bruksenhetsnummer = dwelling-unit number

The last part of the compound is the main noun. Here that is nummer.

-et is the definite singular ending, so it means the.

So:

• et bruksenhetsnummer = a dwelling-unit number
• bruksenhetsnummeret = the dwelling-unit number

The reason it is -et is that the head noun is nummer, which is a neuter noun:

• et nummer
• nummeret

In Norwegian, the definite article is usually attached to the end of the noun instead of appearing as a separate word in front.

So:

• dør = door
• døren = the door

and:

• bruksenhetsnummer = dwelling-unit number
• bruksenhetsnummeret = the dwelling-unit number

That is why the sentence does not need a separate word like English the.

This is a very common Norwegian pattern. When something is written, printed, or visibly displayed somewhere, Norwegian often uses stå rather than være.

So Bruksenhetsnummeret står på døren is idiomatic Norwegian.

You will see the same idea in sentences like:

• Navnet står på listen.
• Prisen står på pakken.
• Det står på skiltet.

English often uses is on, is written on, or says, but Norwegian frequently uses står in these situations.

Står is the present tense of stå, which means stand.

Some useful forms are:

• infinitive: stå
• present: står
• past: sto
• past participle: stått

In this sentence, står means something like is written / is shown / is placed on the door, not literally that the number is standing upright.

Because døren is the definite form, meaning the door.

• en dør = a door
• døren = the door

In this sentence, we are talking about a specific door, so the definite form is natural.

Also, på is the normal preposition here because the number is on the surface of the door.

Yes, it is understandable, but it is less idiomatic.

• står på døren sounds natural when you mean that the number is written, printed, or displayed there.
• er på døren sounds more neutral and less specifically tied to written text.

So a Norwegian speaker would usually prefer står here.

No, this is a normal main-clause word order:

• Bruksenhetsnummeret = subject
• står = verb
• på døren = prepositional phrase

So the pattern is basically:

subject + verb + place/location

Very standard Norwegian.

If you move another element to the front, Norwegian still keeps the verb in second position:

• På døren står bruksenhetsnummeret.

That is a typical Norwegian V2 pattern.

Because they belong to different grammatical genders.

• dør is a common-gender noun: en dør → døren
• nummer is a neuter noun: et nummer → nummeret

So the definite singular ending depends on the noun’s gender:

• common gender often takes -en
• neuter often takes -et

It is more official or administrative than casual.

You are likely to see bruksenhetsnummer in:

• housing documents
• address information
• building registration
• signs in apartment buildings

In everyday conversation, people might sometimes say something simpler like leilighetsnummer if they mean an apartment number, but bruksenhetsnummer is the more official term.

Yes, very often. A useful pattern is:

[something written/displayed] + står + [place]

Examples:

• Navnet står på døren.
• Nummeret står på pakken.
• Adressen står på konvolutten.
• Informasjonen står på nettsiden.

So this sentence is a good model for talking about where written information appears.