"Which historical period is it?"

Translation: Hvilken historisk periode er det?

[hoyastang]

What word do I look to in this sentence to determine that Hvilken should receive an en ending?

[Xneb]

"Periode", it always takes the gender/plurality of the noun it's asking about, so "Hvilket hus bor du i?" = "Which house do you live in?" or "Hvilke bøger har du læst?" = "Which books have you read?"

[JuanMartillo1954]

Wrong answer in danish. The right answer is hvilken historiske periode er det or hvilken periode er det historisk

[Carlos942441]

Why is it "historiske"? Is "hvilken" considered as a determinant here, so that we need to use the det. form of the adjective?