Gene G. answered 06/17/19
You can do it! I'll show you how.
Welches is not properly positioned to be an adjective modifying Behöde.
That would be "Welche Behöde ist ..."
I would translate it simply as "Which is the appropriate office..." "Welches" is a non-gender-specific noun, as is "which". I choose "which" over "which one" because that is true to the word form used in the German. Which and welches are both nouns. in "which one", which is an adjective modifying "one". Having said all that, going from English to German, I would translate both "Which is..." and "Which one is..." as "Welches ist ...", so it's just a picky point anyhow.