A colourless crystalline salt ${}^{\prime }{X}^{\prime }$ is soluble in dilute $HCl$. On adding $NaOH$ solution, it gives a white precipitate which is insoluble in excess of $NaOH$. ${}^{\prime }{X}^{\prime }$ is :

Q. A mixture of two white substances is soluble in water. This solution gives brown colour gas on passing chlorine gas. Another sample of solution gives white precipitate with $BaC{l}_2$ which is insoluble in concentrated $HCl$. The original solution of the mixture gives white precipitate with large excess of $NaOH$ solution whose suspension is used as antacid. After filtering the precipitate, the filtrate was boiled with excess $NaOH$ solution which gave a yellowish precipitate on adding $NaCl{O}_4$. One of the compound of the mixture forms alum. Identify the mixture.

Q. Identify the inorganic salt $A$ whose aqueous solution gives following reactions.
(i) pale yellow precipitate with $AgN{O}_3$ solution, insoluble in dil $HN{O}_3$
(ii) white precipitate with $N{H}_{4}OH$ and also with $NaOH$ solution. However the precipitate does not dissolve in excess of $N{H}_{4}OH$ but soluble in excess of $NaOH$.

Q. Identify the salts $P$ and $Q$ from the observations given below:
When dilute $HCl$ is added to a salt $Q$, a brisk effervescence is produced and the gas turns lime water milky.
When $N{H}_{4}OH$ solution is added to the above mixture (after adding dilute $HCl$), it produces a white precipitate which is soluble in excess $N{H}_{4}OH$ solution.

Q. Identify the cations in each of the following cases :
(i) $NaOH$ solution when added to the Solution (A) gives a reddish brown precipitate.
(ii) $N{H}_{4}OH$ Solution when added to the Solution (B) gives white precipitate which does not dissolve in excess.
(iii) $NaOH$ Solution when added to Solution (C) gives white precipitate which is insoluble in excess.

Q. A colourless crystalline salt, on being heated, gives a colourless gas with a pungent smell. On being passed through an $AgN{O}_3$ solution, this gas forms a white precipitate insoluble in $HN{O}_3$ but readily soluble in an $N{H}_3$ solution. Which of the following reactions can lead to the above observation ?