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 solution is not a buffer solution ?

Options

A. NACN(2 mole)+HCI(1 mole)in 5 L
B. NaCN(1 mole)+HCI(1 mole)in 5 L
C. `NH_(3)(2 mole)+HCI(1 mole) in 5 L`
D. `CH_(3)COOH(2 mole)+KOH(1 mole)in 5 L`