When propionic acid is treated with aqueous sodium bicarbonate, ${\mathrm{CO}}_2$ is liberated. The C from ${\mathrm{CO}}_2$ comes from

${\mathrm{CO}}_2$ comes from ${\mathrm{HCO}}_3^{-}$.

When propionic acid is treated with aqueous sodium bicarbonate, ${\mathrm{CO}}_2$ is liberated. The C from ${\mathrm{CO}}_2$​ comes from bicarbonate.

${\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{COOH}+{\mathrm{NaHCO}}_3\to {\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{COONa}+{\mathrm{H}}_2\mathrm{O}+{\mathrm{CO}}_2\uparrow$

Option D is correct.