Question

1)Al->Na[Al(OH)4]->AlCl3->Al(OH)3->Al2O3->Al
2)Cr2(SO4)3->Cr(OH)3->Cr2O3->Cr->CrCl2->CrCl3->Na[Cr(OH)6]

Answer 1

1)Al(OH)3 + NaOH → Na[Al(OH)4]
Na[Al(OH)4] + 4HCl → AlCl3 + NaCl + 4H2O
AlCl3 + 3NaOH → Al(OH)3 + 3NaCl
2Al(OH)3  t→Al2O3 + 3H2O
2Al2O3 → 4Al + 3O2
2)Cr2(SO4)3 + 6NaOH → 2Cr(OH)3 + 3Na2SO4
2Cr(OH)3    t→Cr2O3 + 3H2O
Cr2O3 + 2Al   t→2Cr + Al2O3
Cr + 2HCl  t→2CrCl2 + H2
4CrCl2 + O2 + 4HCl → 4CrCl3 + 2H2O
CrCl3 + 6NaOH → Na3[Cr(OH)6] + 3NaCl