According to the chemical equation

4KO_2(s) + 2CO_2(g) ---> 2K₂CO_3(s) + 3O_2(g)

a) how many molecules of carbon dioxide react with two formula units of KO₂?

Answer

According to the balanced chemical equation two molecules of carbon dioxide react when four formula units of potassium superoxide react. Carbon dioxide and potassium superoxide always react in this ratio according to this equation. We can use this relationship as a unit conversion factor to convert between potassium superoxide and carbon dioxide.

This conversion between potassium superoxide and carbon dioxide tells us the one molecule of carbon dioxide reacts with two formula units of potassium superoxide.