I don't understand why pupil is singular when "chi" is a plural. Or is it that, as in French, Chi /vous is the formal address.
Yes, chi is the formal singular in the same way as vous is in French.
However in this sentence it's hard to think of a situation where the sentence would begin with 'chi' as a teacher would always use 'ti' to refer to a pupil individually.
A younger pupil might use to to refer to a senior one maybe.