"Is he hungry?"
Translation:O aç mı?
In 'am I happy' the translation was 'mutlu muyum'. I thoght 'mu' was for making a verb a question. In this one, because it is an adjective, we are using 'mi'. So why is this not 'O ac musun?' or why is the other one not 'ben mutlu mi?' (I know I haven't used the right letters).
The particle for making yes/no questions is mI. The vowel is determined only by the last vowel of the word before it, obeying the vowel harmony, it has nothing to do with whether it is a verb or adjective question. This is explained in the notes https://www.duolingo.com/skill/tr/Questions---2