a)\(4Al+3O_2\underrightarrow{t^o}2Al_2O_3\)
\(Al_2O_3+6HCl\rightarrow2AlCl_3+3H_2O\)
\(2AlCl_3+3Ba\left(OH\right)_2\rightarrow2Al\left(OH\right)_3\downarrow+3BaCl_2\)
\(2Al\left(OH\right)_3\underrightarrow{t^o}Al_2O_3+3H_2O\)
\(2Al+3S\underrightarrow{t^o}Al_2S_3\)