Calcium burns in nitrogen to produce a white powder which dissolve in sufficient water to produce a gas (A) and an alkaline solution. The solution on exposure to air produces a thin solid layer of (B) on the surface. Identify the compounds A and B.
(A) C2H2, CaCO3
(B) NH3, CaCO3
(C) NH3, Ca(OH)2
(D) CH4, CaCO3