the clerk will wait on ( whom,who,whomever,whoever) is next. my answer is (whom) is this right

Answer 1

Nope. It should be who or whoever. This pronoun is the subject of the verb "is." In this sentence, "on" is used as an adverb.

Answer 2

"whoever is next" is a noun clause. "will wait on" is the verb... will wait on, think " will help"