What is a buffer solution?
A buffer is a solution that can resist pH change upon the addition of acidic or basic components.
[tex]H_{2}C_{2}O_{4}[/tex] and [tex]HC_{2}O_{4}^{-}[/tex] 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 [tex]H_{2}CO_{3}[/tex] denotes a weak acid and the [tex]KHCO_{3}[/tex] 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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