"From which country?"
Translation:Aus welchem Land?
aus requires the dative case.
Land is neuter.
Put those together and you realise that you need the neuter dative form welchem :)
What's the entire sentence you wrote?
The word welche alone is not a translation of "from which country?".
If your sentence started with aus, remember that that preposition requires the dative case in the following noun phrase; welche is nominative or accusative, feminine or plural, but not dative of any gender.
That would be "From which state?"
"State" (Staat) can be an independent country, but the word "country" (Land) is the usual one in everyday use.
No. Countries are considered as "containers" that you are inside, so if you come from a country, you come from inside the country (aus dem Land) and not from the outside wall of the country (von dem Land).
"Aus welchem Lande" is considered unacceptable. But isn't it just literary usage? If so, it's not really incorrect.
This is just a beginner's course, so we tend to stick to regular, everyday language from the 21st century.
Grammar or forms that are poetic or literary or archaic are generally not accepted in either English or German in this course.
Please stick to everyday language.
"was" is more like "what". "which" is "welche-s/r/m/..." (according to the case and gender). (:
"Was ist es?" = "What is it?"
"Which table?" = "Welcher Tisch" ('der' Tisch) ;
"Which cat?" = "Welche Katze?" ('die' Katze) ;
"Which Sofa?" = "Whelches Sofa?" ('das' Sofa)
But here it's the dative case, because of "aus":
"Aus welcheM Schrank? (der)
"Aus welcheR Box?" (die)
"Aus welcheM Land?" (das)
"Aus welcheN kästeN?" (pl.)
You maybe can better understand here: (It's in French, but you can see the declensions' tables.)