Compound $$\mathrm{P}$$ is neutral, $$\mathrm{Q}$$ gives effervescence with $$\mathrm{NaHCO}_{3}$$ while $$\mathrm{R}$$ reacts with Hinsbergs reagent to give solid soluble in $$\mathrm{NaOH}$$. Compound $$\mathrm{P}$$ is