To determine the empirical formula of potassium nitrate, we need to know the relative proportions of potassium, nitrogen, and oxygen in the compound.

Let's assume we have 1 mole of potassium nitrate. Since each mole of potassium nitrate contains 1 mole of potassium, 1 mole of nitrogen, and 3 moles of oxygen, the relative proportions of these elements are:

Potassium: 1 mole

Nitrogen: 1 mole

Oxygen: 3 moles

Now, we need to find the simplest whole number ratio of these proportions. To do this, we divide each of the mole values by the smallest mole value, which is 1 mole:

Potassium: 1 mole / 1 mole = 1

Nitrogen: 1 mole / 1 mole = 1

Oxygen: 3 moles / 1 mole = 3

Therefore, the empirical formula of potassium nitrate is KNO3.