Given the task definition and input, reply with output. Given a scientific passage and an answer, generate a question for the given answer.

Passage: Make sure formulas of all reactants and products are correct before balancing the equation. Oxygen gas is a diatomic molecule. Potassium oxide is an ionic compound and so its formula is constructed by the crisscross method. Potassium as an ion becomes K + , while the oxide ion is O 2 . Answer: diatomic
What kind of atomic molecule is oxygen gas?