Answer:
Potassium is part of the group 1 metals. Remember that an electron’s configuration is based on where it’s place on the periodic table. For Potassium, K, its grouping in the first column indicates that it will have an oxidation state of +1, when it gives up the electron to try and have a full valence. Its +1 because when it loses the electron, it will end up having more protons than electrons, creating a cation. [ For this case, K has 19 electrons and 19 protons, when it loses the electron to form a bond it results in 19 protons and 18 electrons, creating that +1 I mentioned earlier]. Sulfur is a group VIA nonmetal, which indicates that it will have an oxidation state of - 2, since it easier to take in 2 more electrons, than to try and get rid of the 6 it already has in its valance. Again electrons have a negative charge so when an element takes them in, they end up more negative than positive. Now, K= +1 and S= -2, so a compound between the two is only charge neutral when potassium and sulfur are in a 2:1 ratio. Aka K2S, 2 is a subscript of K.