A 0.1 mol/L aqueous solution of weak monoprotic acid (contains one ionizable hydrogen atom) has a hydrogen ion concentration of 0.001mol/L. The value of Ka is: a) 10-6 b) 10-2 c) 10-3 d) 10-5 I took 0.001 and divided by 0.1 to get 10-2 and I also multiplied them together to get 10-5. That was the only thing I could think of to do. So I know that b) or d) is right. I don't know why though.