A solid compound 'X' on heating gives CO2 gas and a residue. The residue mixed with water forms 'Y' . On passing an excess of CO2 through 'Y' in water, a clear solution, 'Z' is obtained. On boiling 'Z', compound 'X' is reformed. The compound 'X' is

A
${Na}_{2} {CO}_{3}$
B
$K_{2} {CO}_{3}$
C
$Ca {({HCO}_{3})}_{2}$
D
${CaCO}_{3}$

Solution:

The given compound $X$ must be $C a C O_{3} .$ It can be explained by following reactions.

$\underset{(X :}{{CaCO}_{3}} - \overset{Δ}{⟶} \underset{Residue}{CaO} + {CO}_{2} ↑; CaO + H_{2} O \to Ca (OH)_{2}$

$\begin{array}{l} Ca (OH)_{2} + {CO}_{2} + H_{2} O \to \underset{2}{Ca {({HCO}_{3})}_{2}} \\ Ca {({HCO}_{3})}_{2} ⟶ \underset{(X)}{{CaCO}_{3}} + {CO}_{2} ↑ + H_{2} O \end{array}$

A solid compound $' X'$ on heating gives $C O_{2}$ gas and a residue. The residue mixed with water forms $' Y'$ . On passing an excess of $C O_{2}$ through $' Y'$ in water, a clear solution, $' Z'$ is obtained. On boiling $' Z'$ , compound 'X' is reformed. The compound $' X'$ is

Solution:

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