Which of the following words is not a distributive pronoun?

Each, either, neither are distributive pronouns calling attention to the individuals forming a collection and must accordingly be followed by verbs in the singular.
- Each of the scholars has done well.
- Neither of them was invited to the party.
Whether is conjunction.
Example: He asked whether either of the brothers was at home.

Source: High School English Grammar & Composition by Wren & Martin.