Which of the following combinations would create the most effective buffer? So remember with a buffer we talk about buffer range. A buffer is effective as long as the ratio between weak acid and conjugate base is a 12:50 or 1:00 to 10:00 ratio. And we know that the most effective or ideal buffer is when the amount of weak acid is equal to the amount of conjugate base. So weak acid to conjugate base. If you get equal to one, that's the best type of buffer.
So what we're going to do here is we're going to figure out what the ratio is for each of the weak acid conjugate base pairs. The one that has a ratio closest to one would be most ideal and therefore most effective buffer. So if we take a look here in all of these examples, what do we have? Well, we have here is methyl ammonium ion. It is a positively charged amine, which remember positively charged amines are weak acids and then methylamine is just its version with one less H. So this would be the conjugate base.
All we're going to do here is we're going to take the ratios of each of them and see which one comes closest to one that would represent the most ideal buffer. So for A, the ratio of weak acid to conjugate base equals 1.01.2, which comes out to 0.83. For B, what do we have? We have weak acid 0.78 divided by conjugate base 1.3, so this comes out to 0.60. For C, we have 1.5 molar of our weak acid divided by 0.25 molar. So this comes out to 6 and then D, we have 6.8 molar of our weak acid divided by 0.68 molar of our conjugate base. This comes out to 10.
Based on these ratios, the one closest to one is option A. Option A will represent the pairing that is the most ideal buffer and therefore the most effective buffer. Now if they ask us the opposite, which of these options would be the least effective buffer? We'd say option D because option D we have such a vast difference in their concentrations. It's right on the edge of our buffer range, right? So keep in mind for this particular one the answer is option A.