(i) In the given series of reactions, name the compounds X and Z.

(ii) Which type of reaction is X to Z?

(iii) You are given 3 unknown solutions A, B, and C with pH values of 6, 8 and 9.5 respectively. In which solution will the maximum number of hydronium ions be present? Arrange the given samples in the increasing order of H⁺ ion concentration.

(i) X → Sodium hydrogen carbonate (NaHCO₃), Z = Sodium carbonate (Na₂CO₃)

Explanation — When NaCl is treated with CO₂ and NH₃:

NaCl + H₂O + CO₂(↑) + NH₃(↑) → NaHCO₃ + NH₄Cl

Here, X = Sodium hydrogen carbonate (NaHCO₃) and Y = Ammonium chloride (NH₄Cl).

On heating X :

$2 \text {NaHCO}$3 \xrightarrow{\text {Heat}} \text {Na}2 \text {CO}3 + \text H2 \text O + \text {CO}_2(\uparrow)

So, Z = Sodium carbonate (Na₂CO₃)

Hydration of Z gives :

Na₂CO₃ + 10H₂O → Na₂CO₃.10H₂O

So, here Q = Washing soda (Na₂CO₃.10H₂O)

(ii) Thermal decomposition because on heating, sodium hydrogen carbonate decomposes to sodium carbonate, water and carbon dioxide.

(iii) C (pH 9.5) < B (pH 8) < A (pH 6)

Explanation — The pH of a solution is inversely related to its hydrogen ion concentration such that a lower pH value means a higher concentration of hydrogen ions (or hydronium ions) and vice versa.

Among the given solutions — A (pH 6), B (pH 8) and C (pH 9.5) — solution A has the lowest pH therefore, it contains the maximum number of hydronium ions, making it the most acidic of the three.