The compound A on heating gives a colourless gas and a residue thata 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_2CO_3`
C. `K_2CO_3`
D. `CaSO_4.2H_2O`

Answer

A

Explanation

`underset((A))CaCO_3(s)overset(Delta)toCO_2(g)+CaO(s)`
`CaO(s)+H_2O)l)toCa(OH)_2(aq)`
`underset(C)Ca(OH)_2(aq)+underset("excess")2CO_2(g)tounderset(C)Ca(HCO_3)_2(aq)`
`underset(C)Ca(HCO_3)_2(aq)overset(Delta)tounderset(A)CaCO_3(s)+CO_2(g)+H_2O(l)`