Molar concentration of carbonate ion in a solution containing 0.1 mole  ${\text{H}}_{\text{2}}{\text{CO}}_{\text{3}}$  in sufficient water to get 100 ml solution at  ${\text{25}}^{\text{o}}\text{C}$  is  $\text{a x 1}{0}^{\text{b}}$ (in scientific notation and a is adjusted to nearest integer ). What is the value of (a-b)?
For  ${\text{H}}_{\text{2}}{\text{CO}}_{\text{3}},{\text{ K}}_{\text{a1}}=\text{ 4}.0\times \text{ 1}{0}^{-\text{6}}$  and ${\text{K}}_{\text{a2}}=\text{ 5}.0\times \text{ 1}{0}^{-\text{11}}$ .