A mixer of Conc. HCl & Conc. HNO₃ in the ratio of 3:1, is known as “Aqua-Regia”. Gold dissolve only in aqua-regia.

(i)It turns lime water milky. (ii) it extinguishes burning splinter (iii) It dissolves in a solution of sodium hydroxide. (iv) It has a pungent odour.

Ca(OH)₂ (aq) + 2 NH₄Cl (g) → CaCl₂ (s) + 2H₂O (l) + 2NH₃ (g) ↑ So, X = NH₄Cl & Y= 2HO When base Ca(OH)₂ combines with ammonium salt, NH₄Cl, then it liberates ammonia gas and forms calcium ...

In first test tube, the following reactions involves: CaCO₃ + 2HCl → CO₂ + H₂O + CaCl₂ CO₂ Gas is evolved here. In second test tube the following reaction takes place: Zn + 2HCl → ZnCl₂ + H₂

You should know that, when lead nitrate is heated, it decomposes into lead monoxide, nitrogen dioxide and oxygen. Here, reaction is given for understanding: 2Pb(NO₃)₂ (s) → 2PbO(s) + 4NO₂ (g) + O₂ (g)