(2) The carbon-containing gaseous compound that can reduce metals out of ores is carbon monoxide, with the chemical formula: CO;

(3) The substance produced by the Houdebang method of making alkali is sodium carbonate, with the chemical formula: Na2CO3;

(4) 2 atoms of hydrogen. (5) by the representation of ions: in the upper right corner of the elemental symbol indicating the ion, the number of positive and negative charges carried by the ion, the number in the front, positive and negative symbols in the back, with a charge of 1, 1 to be omitted, so that the ammonium root ion symbol: NH4+;

(6) by the elemental valency of the Representation: above the element with a plus or minus sign and a number, plus or minus sign in the front, the number in the back, so the symbol of magnesium with +2 valence is:

The answers are (1) NaHCO3; (2) CO; (3) Na2CO3; (4) 2H; (5) NH4+; (6)