Having thought about this a bit, I think rice is countable in Danish. So if you're talking about the dish or a single rice grain, you'd say “risen”. But if you're talking about eating or cooking rice, you'd say “risene”, because you mean multiple grains of rice. This works because of the suffixed articles. French has something similar I believe. But some confirmation about this whole thing would be great.
My wife is Danish and she says she can't think of a situation where she would use risene. If you want more rice you would ask for 'mere ris' ... mere being 'more' that is 'more rice'. The word 'mere' is used if the next word is NOT COUNTABLE if it was countable, like sweets - candy, then you would ask for flere slik .
I deliberately translated this as 'rices' to see what would happen. It was correct. It should't be. The plain understanding and use of English is rice as a collective noun. We do not eat rices ... usually. Duolingo have marked me as wrong on a previous translation where I answered risen but they wanted risene. There is no context so no way of knowing whether rice is meant as a singular or plural. I get this ... I am English but for students who are working through this from another culture - language, it must be very confusing.
Unfortunately, this is not the only point where at least , as could as it is in general, I doubt about the quality of duolingo. As well for example for word order. Or the cut off for bluetooth connection, now solved, which were fobidding to use headphones. If money could help, one could collect, but in the end it may be a question of the ansatz