Balance the following equations:
(i) $\mathrm{Na}+{\mathrm{O}}_2\underset{}{\to }{\mathrm{Na}}_2\mathrm{O}$
(ii) ${\mathrm{H}}_2{\mathrm{O}}_2\underset{}{\to }{\mathrm{H}}_2\mathrm{O}+{\mathrm{O}}_2$
(iii) $\mathrm{Mg}(\mathrm{OH}{)}_2+\mathrm{HCI}\stackrel{}{\to }{\mathrm{MgCl}}_2+{\mathrm{H}}_2\mathrm{O}$
(iv) $\mathrm{Fe}+{\mathrm{O}}_2\underset{}{\to }{\mathrm{Fe}}_2{\mathrm{O}}_3$
(v) $\mathrm{Al}(\mathrm{OH}{)}_3\underset{}{\to }{\mathrm{Al}}_2{\mathrm{O}}_3+{\mathrm{H}}_2\mathrm{O}$
(vi) ${\mathrm{NH}}_3+\mathrm{CuO}\underset{}{\to }\mathrm{Cu}+{\mathrm{N}}_2+{\mathrm{H}}_2\mathrm{O}$
(vii) ${\mathrm{Al}}_2({\mathrm{SO}}_4{)}_3+\mathrm{NaOH}\underset{}{\to }\mathrm{Al}(\mathrm{OH}{)}_3+{\mathrm{Na}}_2{\mathrm{SO}}_4$
(viii) ${\mathrm{HNO}}_3+\mathrm{Ca}(\mathrm{OH}{)}_2\underset{}{\to }\mathrm{Ca}({\mathrm{NO}}_3{)}_2+{\mathrm{H}}_2\mathrm{O}$
(ix) $\mathrm{NaOH}+{\mathrm{H}}_2{\mathrm{SO}}_4\underset{}{\to }{\mathrm{Na}}_2{\mathrm{SO}}_4+{\mathrm{H}}_2\mathrm{O}$
(x) ${\mathrm{BaCl}}_2+{\mathrm{H}}_2{\mathrm{SO}}_4\underset{}{\to }{\mathrm{BaSO}}_4+\mathrm{HCl}$