Hun er profesjonell.

Because hun is the subject pronoun, meaning it is the person doing or being something in the sentence.

In Hun er profesjonell, hun is the subject of the verb er.

Use henne when the person is the object, for example:

• Jeg kjenner henne. = I know her.
• Jeg så henne. = I saw her.

So:

• Hun er profesjonell. = correct
• Henne er profesjonell. = incorrect

Er is the present tense of å være, which means to be.

So the forms are:

• å være = to be
• er = am / are / is
• var = was / were
• har vært = have/has been

In this sentence, er means is:

• Hun er profesjonell. = She is professional.

Because profesjonell is being used here as an adjective, not a noun.

In Hun er profesjonell, the structure is:

• Hun = she
• er = is
• profesjonell = professional

This is like English She is professional, where professional describes she.

But Norwegian can also use profesjonell as a noun in some contexts:

• Hun er en profesjonell. = She is a professional.

That sentence is grammatical, but it means something slightly different. It identifies her as a professional person, while Hun er profesjonell describes the way she behaves or works.

Because the adjective is in its basic form, which is used with a singular non-neuter subject like hun.

Very roughly:

• profesjonell = basic form
• profesjonelt = neuter singular
• profesjonelle = plural or definite forms in many contexts

Examples:

• Hun er profesjonell. = She is professional.
• Arbeidet er profesjonelt. = The work is professional.
• De er profesjonelle. = They are professional.

So hun takes profesjonell.

In this sentence, it is an adjective.

It describes hun, just like:

• Hun er snill. = She is kind.
• Hun er travel. = She is busy.
• Hun er profesjonell. = She is professional.

But the same word can also be used as a noun:

• en profesjonell = a professional

So the word itself can have more than one function, but here it is clearly an adjective.

Yes, but then it becomes a question.

• Hun er profesjonell. = statement
• Er hun profesjonell? = Is she professional?

Norwegian often forms yes/no questions by putting the verb before the subject.

So:

• statement: Hun er profesjonell.
• question: Er hun profesjonell?

Yes, in some varieties of Norwegian.

• Hun is standard in Bokmål
• Ho is standard in Nynorsk and also used in many dialects

So if you are learning Bokmål, Hun er profesjonell is the expected form.

If you later meet Ho er profesjonell, that is not wrong—it just belongs to a different written standard or dialect background.

A helpful learner-friendly approximation is:

pro-fe-sho-NELL

The last part, -nell, is stressed.

A few things to notice:

• sj in profesjonell sounds like the sh sound in English ship
• the stress falls near the end: profesjoNELL
• Norwegian pronunciation varies by region, so exact vowel quality may differ

A rough English-style pronunciation guide would be:

pro-feh-sho-NELL

Not here.

In Bokmål, adjectives do not change form just because the subject is female. So:

• Han er profesjonell. = He is professional.
• Hun er profesjonell. = She is professional.

The adjective changes mainly for things like:

• neuter singular
• plural

not for male vs. female people.

So profesjonell stays the same with both han and hun.

Yes, it can.

In both languages, the sentence can mean that she behaves in a professional way, especially at work. It often suggests things like being:

• competent
• serious
• well-prepared
• appropriate in behavior

Depending on context, it may describe:

• her attitude
• her work style
• her level of conduct

If you want to say specifically that she works as a professional, Norwegian might also use:

• Hun er en profesjonell.

So the sentence you have is most naturally understood as describing how she is, not just her job title.

Yes, normally Norwegian requires an explicit subject.

So you say:

• Hun er profesjonell.

You do not usually drop hun the way some other languages drop subject pronouns.

That is one important difference from languages such as Spanish or Italian. Norwegian normally keeps the subject pronoun in ordinary sentences.