"Is there a bowl?"
In these sentences が is used instead of は.
Lots of sentences on this course do this, and it should be corrected for beginners or else they will learn incorrectly and build bad habits.
は is a topic particle but if you are asking if an object is present you don't use は、 its always が。unless there's a special condition.
Even though your comment has 103 upvotes, and even though none of the 12 other comments posted since you wrote yours nine months ago have disagreed with you, I'm still going to take the risk and disagree...
I can't say I share the same view as yours at all. In this sentence (and in the other interrogative sentences of this particular kind), to me は seems much more natural to use than が.
(I am just a fellow learner though. However, I'm still fairly certain about this.) ^^
は＆が will throw off even native speakers sometimes, and it really, really depends. In a conversation you can bring most of subjects with は and they're subsequently referred to with が, unless a specific emphasis is made.
It really doesn't help the case that in some cases は can hijack the spot of に or で as well.
If you consider that something is a firm statement you have to search about what you are saying AND respect someone else's thought. We're here to study, not to be showing how superior our knowledge is. If you know he is wrong just correct him respectfully and at least give us better answers.
While I do agree that many of the sentences in Duolingo use は/が in weird ways, I think this specific sentence is fine the way it is.
The difference is small but,
ちゃわんはありますか (Is there a bowl? [Referring to the existence of a bowl])
(Xは)ちゃわんがありますか (Is there a bowl? [In possesion of X, remember that each sentence normally has a noun marked by は whether it be explicit or implied])
Now, of course the first sentence would rarely be used (seeing that we would normally ask this question to see if someone or someplace posesses bowls), but with the lack of our favorite c word, the first would be just as valid. More vivid examples to follow to kinda show what I'm trying to say.
えっ？トイレはありましたか？(What? There was a toilet?) (あなたは)カギがありますか？(Do you have the keys?) エッフェル塔はパリにありますか？(Is the Eiffel Tower in Paris?) (あなたは)ペンがありますか？(Do you have a pen?)