Answer:
This has to do with the charge. The charge of K is +1. The charge of Cl is -1. I like to use a method called the criss cross method. So K+1 and Cl-1. I give each number to the other atom. (the "1" in Cl-1 goes to K the "1" in K+1 goes to Cl) so it becomes K1Cl1 which is KCl. Oxygen has a charge of 2-, so the 2 goes to the K and the 1 in K goes to the O, so it becomes K2O. Dm me if you want further explanation.
Step-by-step explanation: