Water is primarily composed of H+ and OH- ions. The ionic product of water, at 25 oC is 10^-^1^4. Also, conc. of H+ ions = conc. of OH-
Thus, [H+][OH-] = 10^-^1^4 mol/dm3
So, when conc. of [H+] = [OH-] = 10^-^7 mol/dm3.
In this event pH of water will be = -log(H+) = 7
Now, for basic solution, pH > 7. For this purpose, conc. of [OH-] ions must be increased in the solution.
Thus, an increased concentration [OH-] ion characterizes a solution of a base in water
