A white solid (A) when heated liberates a colourless gas which does not support combustion. The residue is dissolved in water to form (B) which can be used for whitewashing. When excess of `CO_2` gas is passed through the solution of (B), it gives a compound {C) which on heating forms (A). Identify (A), (B) and (C). Give the reactions.

Explanation

The observations suggests that the compound (A) is limestone, i.e.,`CaCO_3` , the compound (B) is calcium hydroxide & the compound (C) is calcium bicarbonate. The corresponding reactions are as-
`underset((A))(CaCO_3)overset(Delta)toCaO + CO_2 , CaO + H_2O to underset((B))(Ca(OH)_2)`
`Ca(OH)_2 + CO_2 + H_2O to underset((C))(Ca(HCO_3)_2)`
`Ca(HCO_3)_2 overset(Delta)to CaCO_3 + CO_2 + H_2O`