What's the difference between どこ and なん in this exercise?

Question

I have two exercises which I don't exactly understand. I've already known that どちら is more polite form from どこ. This two could ask about place and "what/which one" ."nan" asks about "kind of company", isn't it? I've checked the answers and it looks like that:

1. A: おくには　なん／どこ　ですか。
   B: タイです。

Correct answer here is "doko" and I suppose it's because of the meaning "what country". Could it be wrong with "nan"?

2. A: かいしゃは　なん／どこ　ですか。
   B: パワーでんきです。

Correct answer is "nan" and I don't understand it! Why it couldn't be "doko"? Please explain me that.

Answer 1

Thanks to @choco's research it's clear that the original right answers are both どこ. Thus if you've been taught as かいしゃはなんですか？ here, something wrong must have happened between the original text and you.

So,

Could it be wrong with "nan"?

Definitely. なん（なに） is only used when you ask about its quality. What you want to know by "What is your country?" usually can also be asked by "Where are you from?", I guess. In this case, the Japanese language always let どこ "where" represent the questioned. You could naturally say どこの国【くに】, どこの町【まち】, どこの会社【かいしゃ】 for "what (lit. where) country/town/company".

If you asked 会社【かいしゃ】はなんですか？ I'd take it as "what kind of company" or "what trade the company belongs to" as best interpretations. If it were お国【くに】はなんですか？, my answer (if I were forced to make one) would be something like "a desert country", "a country of freedom", "a constitutional monarchy country", or whatever.

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PS
As an aside, どちら is also the polite substitute for どれ "which" and どっち "which, either A or B", as well as どこ.

Answer 2

The book Minna no Nihongo 1 says that:

Doko (where) is also used to ask for the name of the country, company, school, organization, etc., that you belong to instead of nan (what). Dochira is more formal than doko.

A: かいしゃは　なん／どこ　ですか。
B: パワーでんきです。

They answered by using a name. That means you need to use doko.

I think if you use なん the question will be "what type of company is ... ?" or "what type of country is ... ?" for [o]kuni, but I do not know if this is accurate.

Answer 3

"なん" <- "何{なに}" which means "what."

"どこ" means "where."

Thus

"かいしゃは　なん ですか。" means "what/which company are you working for?"

whereas

"かいしゃは　どこ　ですか。" means "where is the company you are working for located?"

But I would say

どちら (の会{かい}社{しゃ}) に お勤{つと}めですか?" to mean "what/which company are you working for?"