Correct Answer - D
A buffer solution can be prepared by mixing a weak acid `(CH_(3)COOH)` and its conjugate base `(CH_(3)COO^(-)` form salt) in equal amounts. In practice, a common method of preparing a buffer solution is by partial neutralization of a weak acid solution by adding a strong base solution:
`{:(CH_(3)COOH+,NaOH,rarr,CH_(3)COONa,+H_(2)O),("Initial",2mol,1mol,0,0),("Final",1mol,0mol,1mol,1mol):}`
If an apprecible amount of the weak acid remains unneutralized, then this solution contains significant concentrations of the weak acid and its conjugate base, just as though we had added the salt from a separate solution. Thus, it is a buffer solution. Similarly, we can prepare a buffer by the partial neutralization of a weak base by a strong acid:
`{:(CH_(3)COONa+,HCI,rarr,CH_(3)COOH,NaCI),("Initial",2mol,1mol,0,0),("Final",1mol,0,1mol,1mol):}`