Identify the conjugate acid-base pair respectively from following equilibrium reaction.

$$ \mathrm{HPO}_{4(\mathrm{aq})}^{2-}+\mathrm{H}_2 \mathrm{O}_{(\ell)} \rightleftharpoons \mathrm{PO}_{4(\mathrm{aq})}^{3-}+\mathrm{H}_3 \mathrm{O}_{(\mathrm{eq})}^{+} $$

Which from following nitrogen bases either of purine or pyrimidine does NOT contain $-\mathrm{NH}_2$ group attached with its ring?

Which from following amino acids contains heterocyclic ring at a side chain (R) group?

Calculate the volume occupied by all particles in fcc unit cell if volume of unit cell is $1.6 \times 10^{-23} \mathrm{~cm}^3$.