"Is it breakfast?"
Translation:Est-ce le petit déjeuner ?
"du" is not always or only "some". I thought "du petit-déjeuner" would also be simply "breakfast", so I agree why not "c'est du petit-déjeuner"? Saying "c'est le petit-déjeuner" should be "is it THE breakfast"
You would use "du petit-déjeuner" for "some breakfast" as well as simply "breakfast", but only when adding "some" wouldn't change the sentence (implied some).
For the top posts, often times in English we drop off the word "the", but in French they keep the article (le, etc.).
The English sentence would be clearer if an article was used. There is a world of difference between "is this THE breakfast" and "is this A breakfast."
The first is a question that asks if this food before us we will be eating for breakfast, and the second asks what is this hot trash right here.