Boken blir populær.

In Norwegian, the definite article is often attached to the end of the noun instead of being a separate word.

• bok = book
• boken = the book

So -en here is the definite ending for a singular common-gender noun.

This is very different from English, where you say the book as two words.

Because the sentence is talking about the book, not just a book or book in general.

• bok = a book / book
• boken = the book

So if the meaning shown to the learner is The book is becoming popular or The book becomes popular, then boken is the correct form.

Blir is the present tense of bli, which often means become, get, or come to be.

So:

• bli = to become / to get
• blir = becomes / is becoming / gets

In this sentence, blir populær means something like:

• becomes popular
• is getting popular

The exact English translation depends on context.

Because blir and er are not the same.

• er = is / are
• blir = becomes / is becoming / gets

So:

• Boken er populær = The book is popular
• Boken blir populær = The book becomes popular / is getting popular

If you use blir, the sentence suggests a change or development. The book was not popular before, but now it is becoming popular.

Because this adjective is being used predicatively — that means it comes after a verb like er or blir, rather than directly before the noun.

Compare:

• en populær bok = a popular book
  Here the adjective comes before the noun.

• Boken blir populær = The book becomes popular
  Here the adjective comes after blir.

In predicative position, Norwegian adjectives usually show only the normal agreement pattern:

• common gender singular: populær
• neuter singular: populært
• plural: populære

So boken is singular common gender, which is why populær stays in its basic form.

Yes. Predicative adjectives agree with the noun in number and, in the singular, sometimes gender.

Examples:

• Boken blir populær. = The book becomes popular.
  common gender singular

• Huset blir populært. = The house becomes popular.
  neuter singular

• Bøkene blir populære. = The books become popular.
  plural

So the form populær is correct specifically because boken is singular and common gender.

The dictionary form is bok.

A learner will often want to know all the main forms:

• en bok = a book
• boka / boken = the book
• bøker = books
• bøkene = the books

A useful thing to notice is that the plural changes its vowel:

• bok → bøker

That kind of vowel change is common in some Norwegian nouns.

Because Norwegian usually puts definiteness on the noun itself.

English:

• the book

Norwegian:

• boken

This is one of the most important differences for English speakers learning Norwegian.

Sometimes Norwegian can use both a separate determiner and a definite ending, but that happens in other structures, such as:

• den populære boken = the popular book

In your sentence, there is no adjective before the noun, so boken by itself is enough.

This is the normal Norwegian main-clause word order:

subject + verb + complement

• Boken = subject
• blir = verb
• populær = complement

So the sentence structure is straightforward.

If another element comes first, Norwegian still keeps the verb in second position:

• Nå blir boken populær. = Now the book is becoming popular.

That verb-second pattern is very important in Norwegian.

The letter æ is a separate letter in Norwegian, not just a variation of a.

In populær, it gives a vowel sound somewhat like the a in some pronunciations of cat, though not exactly the same in every dialect.

So populær is not pronounced like English popular. It is a Norwegian word with Norwegian sounds and stress.

A learner should especially notice:

• æ is a real letter in the alphabet
• it appears in many common Norwegian words
• you need to learn it as part of the spelling, not as an optional accent mark

Yes. In natural English, Boken blir populær can often be translated as:

• The book becomes popular
• The book is becoming popular
• The book is getting popular

Which one sounds best depends on context.

That is because Norwegian present tense often covers meanings that English may express with either the simple present or the progressive form. Norwegian does not have a separate verb form exactly like English is becoming.

So blir can fit several natural English translations.