Billedet bliver hængende på væggen, hvis sømmet sidder ordentligt.

It means stays hanging or remains hanging.

This is a very common Danish pattern: blive + position/state word can mean stay/remain in that state.

For example:

• blive stående = stay standing
• blive liggende = stay lying
• blive siddende = stay seated
• blive hængende = stay hanging

So the sentence is not mainly about the picture starting to hang, but about it continuing to hang there.

Hængende is the present participle of hænge.

In Danish, forms in -ende often work a bit like adjectives or state-descriptions:

• stående = standing
• liggende = lying
• siddende = sitting
• hængende = hanging

Here it describes the picture’s state after bliver. So bliver hængende is best understood as remains hanging.

Because hænger and bliver hængende do not mean exactly the same thing.

• Billedet hænger på væggen = the picture is hanging on the wall
• Billedet bliver hængende på væggen = the picture stays hanging on the wall / remains on the wall

So hænger simply describes the current situation, while bliver hængende emphasizes that the situation continues.

In this sentence, that continuing idea fits well with the condition hvis sømmet sidder ordentligt.

No. Here bliver is not a passive marker.

It is the verb blive, which often means become or, in expressions like this, remain/stay.

A real passive with blive would look more like:

• Billedet bliver hængt op = the picture is being hung up

But in bliver hængende, hængende is not a passive form. It describes a state.

Because they are in the definite form: the picture, the nail, the wall.

Danish usually adds definiteness to the end of the noun:

• et billede = a picture
  billedet = the picture

• et søm = a nail
  sømmet = the nail

• en væg = a wall
  væggen = the wall

So instead of a separate word like English the, Danish often uses a suffix.

På væggen means on the wall, referring to a specific wall that is understood from the situation.

• på væggen = on the wall
• på en væg = on a wall

In this sentence, the wall is treated as a known, specific one, so the definite form væggen is natural.

This is a very Danish way of speaking.

The verb sidde often means that something is fixed, positioned, or attached somewhere. It does not only refer to people sitting.

So:

• Sømmet sidder ordentligt means the nail is properly in place, secure, or firmly set

English would usually not say the nail sits properly, but Danish does use sidde this way.

You will see similar uses in sentences like:

• Skruen sidder løst = the screw is loose
• Plakaten sidder på døren = the poster is attached to the door

Here ordentligt means properly, securely, or as it should.

It comes from the adjective ordentlig, which can mean things like proper, decent, or tidy depending on context.

In this sentence it is used adverbially, describing how the nail sits:

• sømmet sidder ordentligt = the nail is sitting properly / is properly secured

The -t form is very common when an adjective is used like an adverb in Danish:

• hurtig → hurtigt
• rolig → roligt
• ordentlig → ordentligt

Because hvis introduces a subordinate clause, and subordinate clauses in Danish do not follow the usual main-clause verb-second pattern.

Compare:

Main clause

• Billedet bliver hængende på væggen

Subordinate clause

• hvis sømmet sidder ordentligt

In the subordinate clause, the subject sømmet comes before the verb sidder.

If you put the hvis clause first, you get:

• Hvis sømmet sidder ordentligt, bliver billedet hængende på væggen.

That is also completely natural.

Because Danish often uses the present tense where English might use will.

So:

• Billedet bliver hængende på væggen can mean the picture stays on the wall or the picture will stay on the wall, depending on context

This is especially common in:

• general truths
• conditions
• schedules
• near-future situations

In a sentence with hvis, English often prefers will in the main clause, but Danish usually does not need a separate future marker.

Yes, but the nuance may change.

For example:

• Billedet hænger på væggen, hvis sømmet sidder ordentligt.
  This sounds more like a general statement about the picture being on the wall.

• Billedet bliver hængende på væggen, hvis sømmet sidder ordentligt.
  This more clearly suggests that the picture will remain there and not fall down.

So the original sentence is a good choice if the idea is the picture stays up as long as the nail is secure.

Hvis means if and introduces the condition.

So the structure is:

• Result/main clause: Billedet bliver hængende på væggen
• Condition: hvis sømmet sidder ordentligt

In other words: the picture remains on the wall on the condition that the nail is secure.

This is one of the most common uses of hvis in Danish.