Many oxidation–reduction reactions can be balanced by inspection. Try to balance the following reactions by inspection. In each reaction, identify the substance reduced and the substance oxidized. a. $\mathrm{Al}(s)+\mathrm{HCl}(a q) \rightarrow \mathrm{AlCl}_{3}(a q)+\mathrm{H}_{2}(g)$ b. $\mathrm{CH}_{4}(g)+\mathrm{S}(s) \rightarrow \mathrm{CS}_{2}(l)+\mathrm{H}_{2} \mathrm{S}(g)$ c. $\mathrm{C}_{3} \mathrm{H}_{8}(g)+\mathrm{O}_{2}(g) \rightarrow \mathrm{CO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(i)$ d. $\mathrm{Cu}(s)+\mathrm{Ag}^{+}(a q) \rightarrow \mathrm{Ag}(s)+\mathrm{Cu}^{2+}(a q)$

a. Balanced equation: \(2\mathrm{Al}(s)+6\mathrm{HCl}(a q) \rightarrow 2\mathrm{AlCl}_{3}(a q)+3\mathrm{H}_{2}(g)\). Oxidized: \(\mathrm{Al}\), Reduced: \(\mathrm{H}\) from \(\mathrm{HCl}\) b. Balanced equation: \(\mathrm{CH}_{4}(g)+2\mathrm{S}(s) \rightarrow \mathrm{CS}_{2}(l)+2\mathrm{H}_{2}\mathrm{S}(g)\). Oxidized: \(\mathrm{C}\) from \(\mathrm{CH}_{4}\), Reduced: \(\mathrm{S}\) c. Balanced equation: \(\mathrm{C}_{3} \mathrm{H}_{8}(g)+5\mathrm{O}_{2}(g) \rightarrow 3\mathrm{CO}_{2}(g)+4\mathrm{H}_{2} \mathrm{O}(l)\). Oxidized: \(\mathrm{C}\) and \(\mathrm{H}\) from \(\mathrm{C}_{3}\mathrm{H}_{8}\), Reduced: \(\mathrm{O}_{2}\) d. Balanced equation: \(\mathrm{Cu}(s)+\mathrm{Ag}^{+}(a q) \rightarrow \mathrm{Ag}(s)+\mathrm{Cu}^{2+}(a q)\). Oxidized: \(\mathrm{Cu}\), Reduced: \(\mathrm{Ag}^{+}\)