A and B have the following reactions: A BC D 1 If C is a commonly used tone in the kitchen

(1) C is a commonly used condiment in the kitchen, so guess C is table salt, adding iron powder to the A solution can produce hydrogen, indicating that A is an acid, according to C is salt, so the acid may be dilute hydrochloric acid, at this time B should be sodium hydroxide, because the reaction of hydrochloric acid and sodium hydroxide can produce sodium chloride, and in line with the form of A + B C + D, so the guess is correct, when hydrochloric acid and sodium hydroxide just react, sodium chloride and water will be generated, at this time the solution is neutral pH = 7, the chemical equation is: HCl + NaOH =NaCl+H2O；

2) B is commonly used to improve acidic soil, it can be seen that B is calcium hydroxide, D is an important chemical raw material and the same category as B, indicating that D is a base, calcium hydroxide and carbon dioxide reaction can produce calcium carbonate and water, so C is calcium carbonate, then A is sodium carbonate, D is sodium hydroxide, in line with A + B C + D and consistent with the description, calcium hydroxide and carbon dioxide reaction equation is: CO2 + Ca(OH)2 = CaCO3 + H2O, calcium carbonate hardness, can be used as a building material;

Therefore, the answer is: (1) dilute hydrochloric acid; =，HCl+NaOH=NaCl+H2O；

2) Na2CO3, building material, CO2 + Ca(OH)2=CaCO3 + H2O