Baking powder (NaHCO3), salt A is commonly used in bakery products. On heating, it forms sodium carbonate (Na2CO3), B and CO2 gas, C is evolved. When CO2 gas is passed through lime water it forms calcium carbonate (CaCO3), which is slightly soluble in water making it milky.
A---NaHCO3; B---Na2CO3; C---CO2 gas