(2) Iron filings react with dilute sulfuric acid to generate ferrous sulfate and hydrogen, and the chemical equation of the reaction is Fe+H2SO4 = FeSO4+H2 ↑; The valence of hydrogen before the reaction is+1, and that after the reaction is 0; The valence of iron before the reaction is 0, and it becomes +2 after the reaction, so the changing elements are hydrogen and iron, and the symbols of the elements are H and Fe.
(3) According to the meaning of the question, if a tablet contains 0. 16g ferrous sulfate as the main component, taking one tablet is equivalent to iron supplementation = 0.16g× 5656+32+16× 4× ≈ 0.06g. 。
So the answer is: (1) AC; (2) hydrogen and iron; (3)0.06.