Explanation: A formation reaction is the formation of ONE mole of product (and no other
products) from its component elements in their standard states. I have made it really
obvious what errors to avoid here so that you know what to look for. When you do this
problem, check to make sure their reactants are in their standard state – here, you have
to know that the standard state of potassium K is solid not gas. Potassium is a metal so
you would guess it’s a solid at 298K and 1 bar (which is roughly 1 atm) …should be
pretty easy. Then, you have to make sure you are only making sure you make only one
product. You should be able to look for these errors even if the answer choices are
different reactions rather than variations of the same, as given here.