(2) The reaction of calcium oxide with water releases a lot of heat, and the heat generated can be collected to heat food. This reaction can be used to prepare hydrated lime, and can also be used as a desiccant to absorb water;

(3) slaked lime is calcium hydroxide with the chemical formula of Ca (OH) 2; According to the algebraic sum of the positive and negative valence of the compound is zero, the valence of iodine can be set as x, then: +2+[x+(-2)×3]×2=0, and the solution is: x =+5;

(4) Calcium carbonate can react with hydrochloric acid to generate carbon dioxide gas, water and calcium chloride. The chemical equation of this reaction can be written as: CaCO3+2HCl ═ CaCl2+H2O+CO2 ↑.

Therefore, the answer is: (1) rickets; (2)ABC； (3) calcium hydroxide; +5; (4)CaCO3+2HCl=CaCl2+H2O+CO2↑。