The hiragana for 中 should be なか, but it is listed as being ちゅう.
The audio plays correctly for this kanji, it is just when asked to select the hiragana that it is incorrect.
It's not incorrect. There are two ways to read any kanji: Onyomi (Chinese-originated reading), and Kunyomi (Japanese reading), with sometimes multiple possible readings under each category. The Onyomi reading for 中 is ちゅう, and the Kunyomi reading is なか. The real issue here is that the current Japanese course wasn't designed in a way that addresses the dual reading of kanji.
Yes, and this has been one of the flaws of the course and a common complaint among the Japanese language learners here. The current course is a bit confusing without external aid. If it's of any help, you can read about Onyomi-Kunyomi reading here:
I clicked this half-expecting another person complaining that the audio pronounces the kanji wrong when it's by itself, where everyone then has to explain the difference between On-yomi and Kun-yomi again and again.
But I agree this is an entirely different issue. It's not wrong at all since naka and chuu are both correct for that kanji, but if Duo expects you to pair the hiragana to a specific audio cue it doesn't make sense to make them not match. I think it is largely Duo isn't capable yet of telling what context a kanji is being used in. It uses a single kun reading when it is being read by itself no matter if the question calls for a different reading or if it's in the context of a word where it should use on-yomi.
This gets especially bad for kanji that have even more readings like 日. It's got 17 different readings depending on the context it is used in but the only audio cue Duo will ever give you is "hi" which makes it difficult when you're trying to break down the pronunciation of a word that takes it.
Having read all these comments I am as confused as ever! I want 中 to be read as なか as that is what the audio keeps saying!!! It is only used in the exercises as part of Tanaka so it is irrelevant (and as I said confusing) that in another context it apparently can represent other sounds. Why can't the duolingo team change it? Don't they check our discussions? (I guess the answer to that is no)