‘Which’ as Interrogative pronoun
Incorrect : Who of the two girls is the taller?
Correct: Which of the two girls is the taller?
Note : The interrogative pronoun "which” refers to both persons and things and asks for one out of a definite number. The pronouns “who” and “what” do not imply any choice.
For example:
Who is going there?
What is your telephone number?