Jeg læser bogen i ro og mag.

Because bogen means the book, while en bog means a book.

In Danish, the definite article is usually attached to the end of the noun:

• en bog = a book
• bogen = the book

So in Jeg læser bogen, the speaker is talking about a specific book.

Læser is the present tense of at læse (to read).

A very common pattern in Danish is:

• infinitive: at læse = to read
• present tense: læser = read / am reading

So:

• Jeg læser = I read / I am reading

It can mean both.

Danish usually uses the simple present where English may use either:

• I read
• I am reading

So Jeg læser bogen could mean:

• I read the book (habitually or generally)
• I am reading the book (right now)

The exact meaning depends on context.

I ro og mag is a fixed expression meaning something like:

• calmly
• without hurrying
• at leisure
• in peace and quiet

So the sentence suggests reading in a relaxed, unhurried way.

It is more idiomatic than translating each word separately.

Mag is not a very common everyday word by itself in modern Danish. Most learners meet it mainly in the expression i ro og mag.

Historically, it has to do with ease, comfort, or leisure. In modern usage, it is best to learn i ro og mag as a whole phrase rather than trying to use mag independently in many situations.

Because the idiom is i ro og mag, not just ro og mag.

The preposition i literally means in, but here the whole phrase functions adverbially, describing how the action happens:

• Jeg læser bogen i ro og mag = I read/am reading the book calmly / at leisure

So i is simply part of the fixed expression.

Yes. This is standard Danish main-clause word order:

• Jeg = subject
• læser = finite verb
• bogen = object
• i ro og mag = adverbial phrase

So the structure is:

Subject + Verb + Object + Adverbial

This is completely natural Danish.

Yes, you can. If you put it first for emphasis, Danish uses verb-second word order:

• I ro og mag læser jeg bogen.

Notice that læser comes before jeg after the fronted phrase. That inversion is normal in Danish main clauses.

Yes, in some contexts you can, but the nuance is slightly different.

• roligt = calmly
• i ro og mag = calmly, unhurriedly, at leisure

So i ro og mag often gives a stronger sense of taking your time and not being rushed. It is a more idiomatic and expressive phrase.

Usually it suggests reading without hurry, in a calm and relaxed way. It can also imply a peaceful atmosphere, but the main idea is the manner of the action rather than the physical location.

So the focus is less where you read and more how you read.