How many grams of potassium chloride are formed by the decomposition of excess potassium chlorate to yield 3.40 L of oxygen?

To determine the grams of potassium chloride formed, you first need to calculate the moles of oxygen produced by the decomposition of potassium chlorate. Then, use the stoichiometry of the balanced chemical equation to convert moles of oxygen to moles of potassium chloride. Finally, from the molar mass of potassium chloride, you can calculate the grams formed.