Is nguo a proper N word? If yes, why does it go with M-pya, and not npya or pya?
Not sure what an 'N word' is (not saying it doesn't exist, I just didn't learn Swahili using English terms so maybe I know it by something else), but it is in the noun class 'I/Zi'. -pya is one of those exceptions to the rule when it comes to this noun class, instead of taking the prefix 'n-' it takes 'm-'. But it always has a prefix.
Some adjectives don't take prefixes for specific noun classes e.g. for 'Li/Ya', '-zuri' is just 'zuri' in singular (e.g. tunda zuri - matunda mazuri)
Thanks. Yes exactly, N-word, like Ndizi. Although calling it a li/ya word is more useful, you're right, because it tells you what prefix to use in the verbs, adjectives, and attributes "of"