To the ear, the ai and ay vowel pairs are identical -- they both make a long a sound. So how can a student distinguish between the two?

A good rule of thumb is to use ay at the end of a word (or the end of the first part of a compound word, or the end of a word before a suffix is added) and ai if it is not at the end of the word. That general principle, while not always perfect, will work with all ten words found here.