Buffer capacity of an acid buffer is maximum when

• A

  ${\mathrm{p}}^{\mathrm{H}}={\mathrm{p}}^{{\mathrm{k}}_{\mathrm{a}}}$

• B

  ${\mathrm{p}}^{\mathrm{H}}={\mathrm{p}}^{{\mathrm{k}}_{\mathrm{a}}}+1$

• C

  ${\mathrm{p}}^{\mathrm{H}}={\mathrm{p}}^{{\mathrm{k}}_{\mathrm{a}}}-1$

• D

  ${\mathrm{p}}^{\mathrm{H}}=7$