What is a buffer solution?
A buffer is a solution that can resist pH change upon the addition of acidic or basic components.
\(H_{2}C_{2}O_{4}\) and \(HC_{2}O_{4}^{-}\) are the pairs which make a good buffer.
The buffer system is a system in which the solution denies change in the ph level i.e. at the time when the acid is added to it. It can be made either in a weak acid and salt or can be a weak base and its salt. Now when the acid is added to a buffer so the ratio is not impacted due to which it does not change sufficient for pH level.
As per the given options, the third one is correct as the \(H_{2}CO_{3}\) denotes a weak acid and the \(KHCO_{3}\) represents the salt. And these two solution does not create any change in the level of pH.
Hence, option A is correct. For B and C, the two substances will react with each other. For A, it can be protons donor and receptor at the same time. So it is a good buffer.
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