Can it be used in singular: макарон? And if it can, does it mean a foodstuff, or does it mean a single noodle?
A single noodle is макаронина. The word макарони was loaned from Italian language (maccheroni ) and is always plural. "Макарон" is genitive case of макарони.
This word is a plural noun (множинний іменник), there isn't a singular form of it. I would translate 'a noodle of pasta' as 'одна трубочка макаронів', however it depends on the shape of the noodle =)
"Whose pasta is this" should also be accepted.
At least right now it's one of the default displayed translations.
Чиї because its more than one piece of pasta? Чий for a single piece?
Because the word макарони is plural.