The formula for potassium and fluorine is KF, which represents potassium fluoride.

Here's why:

* Potassium (K) is in group 1 of the periodic table, meaning it has a +1 charge when it forms an ion (K+).

* Fluorine (F) is in group 17, meaning it has a -1 charge when it forms an ion (F-).

* To form a neutral compound, one potassium ion (K+) combines with one fluorine ion (F-) to balance the charges.