A compound X on heating gives a colourless gas. The residue is dissolved in water to obtain Y. Exces — AITS & Test Series Chemistry Question

Question

A compound X on heating gives a colourless gas. The residue is dissolved in water to obtain Y. Excess CO2 is bubbled through aqueous solution of Y when Z is formed. Z on gentle heating gives back X. The X is (A) CaCO3 (B) Ca(HCO3)2 (C) Na2CO3 (D) NaHCO3 AI