How many liters of fluorine gas, at standard temperature and pressure, will react with 23.5 grams of potium?

You got the correct equation (missing the --> ) so you know you need half as many moles of F2 as you have K. Go to your periodic table and figure out how many moles of K you have, halve that, and then figure out how many liters that many moles of F2 will occupy. I think STP is 22.5 liters per mole, but you better double check your chemistry book on that.