Why is train ticket "bilet na pociąg" but when you say bus ticket you use the adjective "autobusowy", i.e. "bilet autobusowy"? This was in another exercise: "Kupuję bilet autobusowy".
I say "bilet na autobus". And maybe an answer is that we use "pociągowy" in words like "koń pociągowy" (a draft horse), and we avoid the word "pociągowy" to not be misunderstood. Idk, just guessing :). Both "bilet na autobus" and "bilet autobusowy" are natural, but I would choose the first one.
We only accept the declarative word order if there was no "czy" at the beginning of the Polish question.