A solution capable of maintaining its pH relatively constatn, when either excess acid or excess base is added, is said to be buffered While it is not usually considered a buffered solution, a concentrated solution `(10^(-2)` M and higher) of a strong acid or stong base is buffered against large changes in pH when acids or bases are added.
Buffered solutions are usually those containing a wealk acid and a salt of that weak acid or a weak base and the salt of that weak base. For example a solution containing HAc and NaAC resists large change in pH when acid or alkali is added.
For a buffer solution Buiffer capacity is defined as the number of moles of a strong acid or a strong base that causes 1 of the buffer to undergo a 1 unit change in pH. Buffer capacity is maximum when the molar ratio of the two components is unity and the buffer solution is considerred good.
Which species has the lowest concentration in a solution prepared by mixing 0.1 mole each of HCN and NaCN in 1 L solution? `K_(a)(HCN)=10^(-10)`

Options

A. `CN^_(-)`
B. HCN
C. H^(+)
D. `OH^(-)`