Determine whether the following oxidation-reduction reactions ate balanced
correctly, If they are not, provide the correct balanced reaction.
(a) unbalanced:
\(\mathrm{MnO}_{2}(s)+\mathrm{Al}(s) \longrightarrow \mathrm{Mn}(s)+\mathrm{Al}
\mathrm{O}_{3}(s)\) balanced: \(\mathrm{MnO}_{2}(s)+2 A 1(s) \longrightarrow
\mathrm{Mn}(s)+\mathrm{Al}_{2} \mathrm{O}_{3}(s)\)
(b) unbalanced:
\(\mathrm{Cu}(s)+\mathrm{Ag}^{4}(a q) \longrightarrow \mathrm{Cu}^{24}(a q)+A
\mathrm{~g}(s)\) balanced: \(\mathrm{Cu}(s)+2 \mathrm{Ag}^{+}(a q)
\longrightarrow \mathrm{Cu}^{2+}(a q)+2 \mathrm{Ag}(s)\)
(c) unbalanced:
$$
\mathrm{Br}^{-}(a q)+\mathrm{MnO}_{4}^{-}(a q) \rightarrow
\mathrm{Br}_{2}(d)+\mathrm{Mn}^{2+}(a q)
$$
(icidic solution)
balanced:
$$
\begin{aligned}
16 \mathrm{H}^{+}(a q)+10 \mathrm{Br}^{-}(a q)+& 2 \mathrm{MnO}_{4}^{-}(a q)
\longrightarrow \\
& 5 \mathrm{Br}(l)+2 \mathrm{Mn}^{2+}(a q)+8 \mathrm{H}_{2} \mathrm{O}(l)
\end{aligned}
$$
(d) unhalanced:
$$
\begin{aligned}
&\mathrm{MnO}_{4}(a q)+\mathrm{S}^{2-}(a q) \rightarrow
\mathrm{MnS}(s)+\mathrm{S}(s) \quad \text { (basic solution) } \\
&\text { balanced: } \\
&8 \mathrm{H}^{-1}(a q)+\mathrm{MnO}_{4}^{-}(a q)+\mathrm{S}^{2-}(a q)
\rightarrow \\
&\qquad \mathrm{S}(s)+\mathrm{MnS}(s)+4 \mathrm{H}_{2} \mathrm{O}(l)
\end{aligned}
$$
