A compound X on heating gives a colourless gas. This residue is dissolved in water to obtain Y. excess `CO_(2)` is bubbled through aqueous solution of Y, Z is formed. Z on gentle heating give back X. the X is

The compound X on heating gives a colourless gas. The residue is dissolved in water to obtain Y Excess CO_2 is bubbled through aqueous solution of Y, Z is formed. Z on gentle heating gives back X. The compound X is:

The compound (X) on heating gives a colourless gas a nd a residue that is dissolved in water to obtain (B). Excess of CO_2 is bubbled through aqueous solution of B, C is formed. Solid (C) on heating gives back X. (B) is

The compound 'A' on heating gives a colourless gas and a residue. The residue dissolves in water to obtain (B). When excess of CO_(2) is bubbled through aqueous solution of B gentle heating gives back A. Compound 'C' is