A solid compound `'X'` on heating gives `CO_(2)` gas and a residue. The residue mixed with water forms `'Y'`. On passing an excess of `CO_(2)` through `'Y'` in water , a clear solution, `'Z'` is obtained. On boiling `'Z'`, compound `'X'` is reformed. The compound `'X'` is

Options

A. `Na_(2)CO_(3)`
B. `K_(2)CO_(3)`
C. `Ca(HCO_(3))_(2)`
D. `CaCO_(3)`

Answer

D

Explanation

The given compound X must be `CaCO_(3)`. It can be explained by following reaction
`underset("(X)")(CaCO_(3)) overset(Delta)to underset("Residue")(CaO) +CO_(2) uarr , CaO +H_(2)O to underset("(Y)")(Ca(OH)_(2))`
`Ca(OH)_(2) +CO_(2) +H_(2)O to underset("Z")(Ca(HCO_(3))_(2))`
`Ca(HCO_3)_(2) overset(Delta)to underset("(X)")(CaCO_(3))+CO_(2) uarr +H_(2)O`