Question

State why the valency of the metal potassium is +1 and of the non-metal chlorine is -1.

Answer 1

Metal potassium (K) has 1 electron in the outer most shell which it loses and becomes K+ has valency [+1] whereas
Non-metal chlorine [Cl] has 7 electrons in the valence shell and gains 1 electron and becomes [Cl^–] has valency [-1]