I think everyone’s thread here is answered by the DL dictionary — I put ‘the medium soda’ too. https://www.duolingo.com/dictionary/Hawaiian/i/fd6016eb46b47c6406919c424f53d3be
Which is to say “i” means “a”, “on” or “towards”.... in this case the indefinite article “a”.
I hope this is right!
I don’t believe that’s right. I think that is a special use of “i”, followed by “naʻu”. This is a useful read:
Unfortunately it does not explain this exact situation. I think the “i” is the normal direct object marker. I would hazard a guess that “kekahi” would be technically correct as a kaʻi but that it might be left off in conversation.