Which equilibrium expression represents the ionization of water?

The equilibrium constant expression for this reaction that takes place in water and involve ions can be written as K=  [H_3 O^+ ][OH^- ]/([H_2 O]  ^2 ). But the concentration of undissociated water, H_2 O is much larger than the concentration of the ions that is essentially remains constant. Therefore, we can include it in the equilibrium constant. The resulting new equilibrium constant can be written:  K_W= [H_3 O^+ ][OH^- ].

explanation: it gains negative electrons, therefore becoming negatively charged. as charge cannot be created, nor destroyed, only transferred, this leaves the wool positive. now that they have opposite charges, the two items attract.