Compounds which are more acidic then ${\mathrm{H}}_2{\mathrm{CO}}_3$, gives ${\mathrm{CO}}_2$ gas on reaction with ${\mathrm{NaHCO}}_3$. Compound $\mathrm{B}$ i.e. Benzoic acid and compound $\mathrm{C}$ i.e. picric acid both are more acidic than ${\mathrm{H}}_2{\mathrm{CO}}_3$.

equilibrium favours forward direction and ${\mathrm{CO}}_2\uparrow$ is liberated.

Equilibrium favours backward direction and ${\mathrm{CO}}_2\uparrow$ is not liberated.