"Is that a chair?"

Translation: Az egy szék?

[ZelvaCZ]

I wrote "Az egy szék van" - is the "van" wrong, or just unnecessary and not added to the list of possible solutions yet?

[Apahegy]

You don't need to use a form of "to be" in this case- van when a sentence is merely stating what or how something is.

So "This is a chair" is just "Ez (egy) szék," and "This chair is tall" would be "Ez a szék magas."

You do however use van when the sentence has an adverb or a question, such as "Hol van a szék?" - "A szék itt van."

[IsacharJones]

Would 'Az egy szék?' also be correct here?

[MamshieCla]

Also my question

[jzsuzsi]

Of course, it is correct.