* Oxygen (O) exists as a gas at room temperature. Gases are generally poor conductors of electricity.

* Zinc (Zn) is a metal. Metals are excellent conductors of electricity and are typically malleable (not brittle).

* Iodine (I) is a non-metal. Non-metals are generally poor conductors of electricity and often exist as brittle solids.

Key takeaway: The properties of being a poor conductor and brittle are associated with non-metals, making iodine the likely candidate.