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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 is

Options

  1. ACaCO 3
  2. BNa 2 CO 3
  3. CK 2 CO 3
  4. DCaSO 4 ·2H 2 O

Correct answer

A. CaCO 3

Step-by-step solution

The reactions can be summarised as follows : A → Δ Colourless gas + residue Residue + H 2 O → B → Excess CO 2 C → Δ A This is possible only when A is CaCO 3 . The reactions are as follows : CaCO 3 → Δ CO 2 + CaO A Colourless gas Residue CaO + H 2 O → Ca OH 2 → excess CO 2 Ca HCO 3 2 → Δ CaCO 3 B C A

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