Identify conjugate acid and conjugate base for $\mathrm{HCO}_3{ }^{-}$ion respectively

To determine the conjugate acid and conjugate base of $\mathrm{HCO}_3^{-}$, consider its amphoteric nature—it can either accept or donate a proton ($\mathrm{H}^{+}$).

As a base, $\mathrm{HCO}_3^{-}$ accepts $\mathrm{H}^{+}$ to form its conjugate acid: $\mathrm{HCO}_3^{-} + \mathrm{H}^{+} \rightarrow \mathrm{H}_2\mathrm{CO}_3$.

As an acid, $\mathrm{HCO}_3^{-}$ donates $\mathrm{H}^{+}$ to form its conjugate base: $\mathrm{HCO}_3^{-} \rightarrow \mathrm{H}^{+} + \mathrm{CO}_3^{2-}$.

The conjugate acid is $\mathrm{H}_2\mathrm{CO}_3$ and the conjugate base is $\mathrm{CO}_3^{2-}$.

Evaluating the options:
Option A: $\mathrm{CO}_3^{2-}$ and $\mathrm{H}_2\mathrm{CO}_3$ (incorrect order)
Option B: $\mathrm{H}_2\mathrm{CO}_3$ and $\mathrm{CO}_2$ (incorrect conjugate base)
Option C: $\mathrm{CO}_2$ and $\mathrm{H}_2\mathrm{CO}_3$ (both incorrect)
Option D: $\mathrm{H}_2\mathrm{CO}_3$ and $\mathrm{CO}_3^{2-}$ (correct).

The answer is $\boxed{\text{D}}$.