Question

The compound A on heating gives a colourless gas and a residue that is 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 A is -

• A. ${Na_2 CO_3}$
• B. ${K_2 CO_3}$
• C. ${CaSO4.2H2O}$
• D. ${CaCO_3}$

Answer 1

Answer: (D)

${CaCO_3}$

Answer 2

Given,
Thus, the compound $'A'$ must be $CaCO_3$ and the reactions are as follows