The compound A on heating gives a colourless gas and a residue that is dissolved in water to obtain B. Excess of `CO_(2)` is bubbled through aqueous solution of B,C is formed which is recovered in the solid form.Solid C on gentle heating gives back A. The compound is

Options

A. `CaCO_(3)`
B. `Na_(2)CO_(3)`
C. `K_(2)CO_(3)`
D. `CaSO_(4) . 2 H_(2)O`

Answer

A

Explanation

`underset((A))(CaC)O_(3)(s) overset(Delta)(to) CO_(2) (g) + CaO(s)`
`CaO (s) + H_(2)O (l) to underset((B))(Ca(OH)_(2)) (aq)`
`underset((B)) (Ca(OH)_(2)) (aq) + underset(("excess"))(2 CO_(2)) (g) to Caunderset((C))((HCO_(3))_(2)) (aq) `
`Caunderset((C))((HCO_(3))_(2)) (aq) overset(Delta)(to) Ca underset((A))(CO_(3)) (s) + CO_(2) (g) + H_(2)O(l)`