Postadressen er ny.

Because postadressen is the definite singular form: the postal address.

• postadresse = a postal address
• postadressen = the postal address

In Norwegian, definiteness is usually added to the end of the noun:

• en bil = a car
• bilen = the car

So here, -en makes the noun definite.

The ending -en is a common definite ending for singular nouns in Bokmål.

Here the noun is being used as an en-word/common-gender noun:

• en postadresse = a postal address
• postadressen = the postal address

A learner may notice that some nouns can also appear with other gender patterns in Norwegian, but in this sentence the form chosen is postadressen.

Er is the present tense of å være (to be).

So:

• er = is / am / are, depending on context

In this sentence, Postadressen er ny follows the very common pattern:

noun + er + adjective

That is the Norwegian equivalent of The postal address is new.

Because ny agrees with a singular common-gender noun.

Here is the pattern for new:

• ny → singular common gender
• nytt → singular neuter
• nye → plural, and also many definite/modified uses before a noun

Examples:

• en bil er ny = a car is new
• et hus er nytt = a house is new
• bilene er nye = the cars are new

Since postadressen is singular and treated here as common gender, ny is correct.

Good question. That is because ny here is a predicate adjective: it comes after the verb er.

In Norwegian, adjectives behave differently depending on where they appear:

1. Before the noun (attributive):

   • den nye postadressen = the new postal address

2. After the verb (predicate):

   • postadressen er ny = the postal address is new

So even though postadressen is definite, the adjective stays ny here because it is not directly in front of the noun.

The word order is:

Subject + verb + adjective

So:

• Postadressen = subject
• er = verb
• ny = adjective

This is a very normal Norwegian sentence pattern, especially in simple statements.

Usually, no, not in a neutral sentence.

Postadressen er ny is the natural way to say The postal address is new.

If you say den postadressen, it usually sounds like that postal address rather than just the postal address.

Compare:

• postadressen er ny = the postal address is new
• den postadressen er ny = that postal address is new or a marked/emphatic form

So for a normal definite noun, the suffix on the noun already does the job.

You would use the indefinite noun:

En postadresse er ny.

That means A postal address is new.

Compare:

• En postadresse er ny = A postal address is new
• Postadressen er ny = The postal address is new

So the main change is:

• en postadresse = indefinite
• postadressen = definite

Yes. Norwegian very often forms compound nouns as a single word.

Here:

• post = mail/post
• adresse = address
• postadresse = postal address / mailing address

This is very common in Norwegian, and English speakers often need to get used to writing such combinations as one word.

A simple learner-friendly approximation is:

POHST-ah-dress-en ehr nee

A few helpful points:

• postadressen has the stress near the beginning
• er is often pronounced quite lightly in normal speech
• ny sounds like nee, but with a rounded Norwegian vowel

The exact pronunciation varies a bit by dialect, but that approximation is good enough to start with.