Why is a reaction between Sodium and Potassium impossible?

it is because a number of factors, including sample surface cleanliness and temperature, can prevent chunks of alkali metals from exploding on contact with water. The team eliminated those variables and others by using a sodium-potassium alloy that remains liquid at room temperature and a droplet delivery system featuring a calibrated syringe.

Potassium has a chloride mixture which makes it so sodium interacts easily with it to form the bond

that tool would be a compass