18.
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 which result in the formation of Z. Z on gentle heating gives back X. The compound X is:
A:
CaCO3
B:
Na2CO3
C:
Ca(HCO3)2
D:
K2CO
The answer is:
A
