c
\(HA ⇌  H^+ + A^-\)   \(K\)=\(\frac{{\left[ {{H^{_ + }}} \right]\,\,\,\left[ {{A^ - }} \right]}}{{\left[ {HA} \right]}}\)

નિર્બળ એસિડનું પ્રબળ બેઇઝ વડે તટસ્થીકરણ કરતાં, \(HA  +  OH^-  ⇌ A^-  +  H_2O\)

તો \(\,{\text{K}}\,\, = \,\,\,\frac{{\left[ {{{\text{A}}^{\text{ - }}}} \right]}}{{\left[ {HA} \right]\,\,\,\,\left[ {O{H^ - }} \right]}}\,\,\,.........\,\,(ii)\)

\((i)\) ને \((ii)\) વડે ભાગતા,\(\,\frac{{{{\text{K}}_{\text{a}}}}}{{\text{K}}}\,\, = \,\,\left[ {{H^ + }} \right]\,\left[ {O{H^ - }} \right]\,\, = \,\,{K_w}\,\,\,\,\,\,\,\therefore \,\,K\,\, = \,\,\frac{{{K_a}}}{{{K_w}}}\,\, = \,\,\frac{{{{10}^{ - 5}}}}{{{{10}^{ - 14}}}}\,\, = \,\,{10^9}\)