Are both Samhain and Mí na Samhna acceptable for saying November, or is there a time when one is more accepted/appropriate?
Depending upon the context, use of Mí na Samhna could avoid a possibility of confusion with the ancient festival Samhain. In general, Sahmain seems to be usable as “November” without confusion.
I assume that in the context of this exercise, both Samhain and Mí na Samhna should be acceptable answers.
is mi na samhain= the month of november?
no, you have to put Samhain in to the genitive so it would be " Mí na Samhna"
Why "na" instead of "an"?
Samhain is a feminine noun, and feminine nouns use na as the singular definite article in the Genitive case - some other examples are Uachtarán na hÉireann, Cat na scoile, Biachlár na bialainne.