In English, "an egg" is a countable noun (the things that come out of certain animals) and just "egg" is a mass noun (the edible stuff found inside eggs).
More generally, English requires articles ("a/an" or "the") or some other determiner ("this", "some," etc.) in most cases, especially in the singular. Mass nouns are a specific exception.
Yes, "egg" can be used as a mass noun in this context. Examples:
(In all cases, when I call something "topical" below, I mean it's been established in recent usage as a subject of conversation)
"I am eating an egg:" eating one non-topical egg.
"I am eating egg:" eating some amount of (non-topical) stuff inside eggs.
"I am eating the egg:" probably eating one topical egg. Or, eating some amount of the stuff inside eggs, if that stuff is topical.
"I am eating eggs" or "I am eating some eggs:" eating several non-topical eggs.
"I am eating the eggs:" Eating several topical eggs.
All of which is distinct from:
"I eat eggs / I eat egg:" As a generalization, eggs (or the stuff inside them) are a thing I'm willing to eat.
There is, but it's... higher level of Polish. There are some, let's call them, 'habitual verbs', and their name says it all. "jadać" is a habitual form of "jeść", so if you regularly eat eggs, you can say "Jadam jajka".
But "jem jajka" is perfectly fine for both those English sentences.
Ehm... if you translate from English, then both versions are equally correct. But if you have a 'type what you hear' exercise, how could both be correct? You heard one of them. Not the other. Of course the other is wrong. 'type what you hear' exercise will always have only one correct answer - the exact sentence that was said.
It also cannot be a matter of consistency, because both types of exercises are based on the exactly same sentence with the exact same answers. They aren't put separately.
On a separate notion, I'm confused that you put this comment in the PL->ENG exercise discussion. Oh, and also the basic sentence (the one that was put in the Incubator and for which there is an audio file) is "Jesz jajko i pijesz herbatę", not the plural one.
I put it in this one because I noticed the use of Jesz not Jecie for this particular test but i still believe that, when you're asked to translate the English to Polish tests, both versions of "you" should be accepted. The fact is that one test has the singular as the correct answer (given at top of thread) and the other plural. I don't see any reason for both jesz/jecie not being right in these tests. I just want all tests to be consistent.
That's the thing, it does matter. If I am going to learn Polish then I have to be given the right information. If I am being marked wrong, when I'm not, how am I supposed to learn, and improve, my Polish. To me, if you want to learn a language then you have to do it right. That can't happen if you're being told what you typed is wrong only to see another test show the sentence you were told is wrong. I might as well give up learning this language, or at least give up on Duolingo. Shame, because the app actually works in that words have stuck, which other courses have not succeeded in doing.