Describe the laboratory preparation for the following gases: (a) hydrogen, (b) oxygen, (c) carbon dioxide, (d) nitrogen. Indicate the physical states of the reactants and products in each case. [Hint: Nitrogen can be obtained by heating ammonium nitrite \(\left(\mathrm{NH}_{4} \mathrm{NO}_{2}\right)\).]

1. Hydrogen: It's prepared by the reaction of zinc metal with dilute hydrochloric acid: \[ \mathrm{Zn(s) + 2HCl(aq) \rightarrow ZnCl_{2}(aq) + H_{2}(g)} \] 2. Oxygen: It's prepared by the decomposition of hydrogen peroxide: \[ 2\mathrm{H}_{2}\mathrm{O}_{2}(aq) \rightarrow 2\mathrm{H}_{2}\mathrm{O}(l) + \mathrm{O}_{2}(g) \] 3. Carbon Dioxide: It's prepared by the reaction of calcium carbonate with hydrochloric acid: \[ \mathrm{CaCO}_{3}(s) + 2\mathrm{HCl}(aq) \rightarrow \mathrm{CaCl}_{2}(aq) + \mathrm{CO}_{2}(g) + \mathrm{H}_{2}\mathrm{O}(l) \] 4. Nitrogen: It's prepared by the heating of ammonium nitrite: \[ \mathrm{NH}_{4}\mathrm{NO}_{2}(s) \rightarrow \mathrm{N}_{2}(g) + 2\mathrm{H}_{2}\mathrm{O}(g) \]