Translation:They put at most two chairs in each room.
There is no "seat" in that sentence, however, the last time I came across this question the word "cadeira" was there. I think it's just omitted from some variations of this question. That was the first time I saw "cadeira" in these variations, and the ones without it don't usually mark you wrong if you omit "chair/cadiera". Usually, because sometimes Duo thinks you're a mind reader
I reported this omission. Not that it will make any difference. I wonder, would a native speaker know that they're referring to seats?
1) it does make a difference, I get emails when my suggestions and corrections have been accepted.
2) it probably depends on context. If you were standing in a room full of chairs and telling someone about how many are put in the room, they'd get it
It saying I missed a word. Seats... this word does not show up in the original sentence.
As you can see from the comments, you need to report it and move on. The next time you come across it, even if you choose the right answer, report it anyway.