Buffer solutions have constant acidity and alkalinity because

Options

A. these given unionised acid or base on reaction with added acid or alkali
B. acids and alkalies in these solutions are shielded from attack by other ions
C. they have large excess of `H^(+)` or `OH^(-)` ions
D. they have fixed value of `pH`

Answer

A

Explanation

If small amount of an acid or alkali added to a buffer solution, it converts them into unionised acid or base. Thus, its pH remains unaffected or in other words its acidity/alkalinity remains constant. e.g.
`H_(3)O^(+)+A^(-)hArr H_(2)O+HA`
`.^(-)OH+HA rarr H_(2)O+A^(-)`
If acid is added, it reacts with `A^(-)` to form undissociated H A. Similarly, if base/alkali is added, `OH^(-)` combines with H A to give `H_(2)O` and `A^(-)` and thus, maintains the acidity/alkalinity of buffer solution.