A solution $\mathrm{P}$ has a $\mathrm{pH}=13$, solution $\mathrm{Q}$ has $\mathrm{pH}=6$, and solution $\mathrm{R}$ has $\mathrm{pH}=2$. Which solution will liberate ammonia gas from ammonium sulphate on heating?

Name the chemical which should be added to sodium chloride, so as to obtain hydrogen chloride. 

State your observation when hydrogen chloride mixes with ammonia. 

Name the experiment which shows the high solubility of hydrogen chloride.