Na końcu sali stoi siedemnaście krzeseł dla rodziców.

Because siedemnaście krzeseł is a numeral phrase with a number above 4. In Polish, phrases like pięć krzeseł, dziesięć książek, siedemnaście krzeseł are often treated as a single quantity, so the verb is usually 3rd person singular in neutral descriptions.

So Polish says:

• stoją trzy krzesła = three chairs are standing
• stoi pięć krzeseł = five chairs are standing
• stoi siedemnaście krzeseł = seventeen chairs are standing

That is why you get stoi, not stoją.

After numbers 5 and higher, Polish normally uses the genitive plural of the noun.

So:

• krzesło = singular dictionary form
• krzesła = nominative plural
• krzeseł = genitive plural

Because the sentence has siedemnaście, the noun must be krzeseł.

Because the phrase means at the end of the room/hall. In Polish, that structure is built as:

• na końcu = at the end
• sali = of the room/hall

So sali is there because it depends on koniec: the end of the hall.

A useful way to see it is:

• koniec sali = the end of the hall
• na końcu sali = at the end of the hall

Because na końcu is the normal expression for a physical location meaning at the end or at the back.

By contrast, w końcu usually means things like:

• finally
• at last
• in the end

So:

• na końcu sali = at the end of the hall
• w końcu = finally

They look similar, but they mean different things.

Polish often uses a position verb where English would simply say there is/are.

With objects like chairs, tables, bottles, lamps, etc., Polish often uses:

• stać = to stand
• leżeć = to lie
• wisieć = to hang

So stoi siedemnaście krzeseł sounds natural because chairs are thought of as objects standing somewhere.

You could also say jest tam siedemnaście krzeseł, but that sounds more like simple existence: there are seventeen chairs there. Stoi gives a more physical, spatial picture.

Rodziców is genitive plural because the preposition dla always takes the genitive.

So:

• rodzice = nominative plural, parents
• rodziców = genitive plural, used after dla

That is why Polish says:

• dla rodziców = for parents / for the parents

Even though English uses for, Polish does not use the dative here.

It can mean either, depending on context, because Polish has no articles.

So dla rodziców could mean:

• for parents
• for the parents

In a real situation, context tells you whether it is general or specific. Very often in a sentence like this, it means chairs intended for the parents present at some event.

Yes. Polish word order is quite flexible because the endings show the grammatical relationships.

The original sentence:

• Na końcu sali stoi siedemnaście krzeseł dla rodziców.

is very natural if you want to start with the location.

You could also say:

• Siedemnaście krzeseł dla rodziców stoi na końcu sali.

That is still grammatical, but it puts more focus on the seventeen chairs.

So the meaning stays basically the same, but the emphasis changes.

Because Polish does not have articles like a and the.

Polish relies on context instead. So the sentence can be understood as something like:

• At the end of the hall stand seventeen chairs for parents
• At the end of the hall, there are seventeen chairs for the parents

English must choose an article; Polish does not.

That is a very useful comparison:

• Na końcu sali stoi jedno krzesło. = One chair is at the end of the hall.
• Na końcu sali stoją dwa krzesła. = Two chairs are at the end of the hall.
• Na końcu sali stoją trzy krzesła. = Three chairs are at the end of the hall.
• Na końcu sali stoją cztery krzesła. = Four chairs are at the end of the hall.
• Na końcu sali stoi pięć krzeseł. = Five chairs are at the end of the hall.

So the big pattern is:

• 1: singular noun, singular verb
• 2–4: nominative plural noun, plural verb
• 5+: genitive plural noun, usually singular verb in this kind of sentence

That pattern explains both stoi and krzeseł in your sentence.