${\mathrm{Ka}}_1,{\mathrm{Ka}}_2$ and ${\mathrm{Ka}}_3$ are the respective ionization constants for the following reactions $\left(\mathrm{a}\right),\left(\mathrm{b}\right)$ and $\left(\mathrm{c}\right)$.

(a) ${\mathrm{H}}_2{\mathrm{C}}_2{\mathrm{O}}_4\rightleftharpoons {\mathrm{H}}^{+}+{\mathrm{HC}}_2{\mathrm{O}}_4^{-}$

(b) ${\mathrm{HC}}_2{\mathrm{O}}_4^{-}\rightleftharpoons {\mathrm{H}}^{+}+{\mathrm{HC}}_2{\mathrm{O}}_4^{2-}$

(c) ${\mathrm{H}}_2{\mathrm{C}}_2{\mathrm{O}}_4\rightleftharpoons 2{\mathrm{H}}^{+}+{\mathrm{C}}_2{\mathrm{O}}_4^{2-}$

The relationship between ${\mathrm{K}}_{{\mathrm{a}}_1},{ \mathrm{K}}_{{\mathrm{a}}_2}$ and ${\mathrm{K}}_{{\mathrm{a}}_3}$ is given as

• A

  ${\mathrm{K}}_{\mathrm{a}3}={\mathrm{K}}_{\mathrm{a}1}+{\mathrm{K}}_{\mathrm{a}2}$
• B

  ${\mathrm{K}}_{\mathrm{a}3}=\frac{{\mathrm{K}}_{\mathrm{a}1}}{{\mathrm{K}}_{\mathrm{a}2}}$
• C

  ${\mathrm{K}}_{\mathrm{a}3}={\mathrm{K}}_{\mathrm{a}1}-{\mathrm{K}}_{\mathrm{a}2}$
• Correct answer
  D

  ${\mathrm{K}}_{\mathrm{a}3}={\mathrm{K}}_{\mathrm{a}1}\times {\mathrm{K}}_{\mathrm{a}2}$

Hence, the correct answer is option: 'D'.