When potassium (K) and chlorine (Cl) combine, they form potassium chloride (KCl).

This is a classic example of an ionic compound. Here's why:

* Potassium (K) is a metal and tends to lose one electron to become a positively charged ion (K+).

* Chlorine (Cl) is a nonmetal and tends to gain one electron to become a negatively charged ion (Cl-).

These oppositely charged ions attract each other, forming an ionic bond. The resulting compound, potassium chloride, is a white crystalline solid commonly used as a salt substitute and in fertilizers.