When hydrochloric acid is added to marble pieces, a gas (A) is evolved. On passing gas A through lime water, a white precipitate of (B) is formed. When excess of A is passed, B dissolves due to the formation of soluble C. Identify A, B and C. Explain the reactions.

Chemical Reactions:
Marble is calcium carbonate. It reacts with HCl to give CO₂
CaCO₃ + 2HCl $\underset{ }{\to }$ CaCl₂ + CO₂ + H₂O
Marble                                             (A)

CO₂ when passed through lime water [Ca(OH)₂] gives a white precipitate of CaCO₃.
Ca(OH)₂ + CO₂(g) $\underset{ }{\to }$CaCO₃(s) + H₂O
                                             White ppt.
                                                  (B)
On passing excess CO₂, CaCO₃ dissolves forming soluble Ca(HCO₃)₂.
CaCO₃ + CO_{2 $\stackrel{+{\mathrm{H}}_2\mathrm{O}}{\to }$} Ca(HCO₃)₂ (aq)
                                   Calcium
                                   hydrogen
                                   carbonate
                                       (C)

A — Carbon dioxide
B — Calcium carbonate
C — Calcium hydrogen carbonate