question_answer

      (a) Aluminium oxide is amphoteric oxide (b) Metal displace hydrogen gas from acids (c) Iron articles are frequently painted (d) Iron sheets are coated with zinc layer (e) Lemon or tamarind juice are effective in cleaning tarnished copper vessels.

Answer:

                  (a) Aluminium oxide is amphoteric oxide because it shows the properties of both acidic and basic oxides. It reacts with both acids and bases to form salt and water.                        (1) (b) Metals when react with acids, donate electrons to hydrogen ions present in acid to form hydrogen atoms which combines further form hydrogen gas.                                      (1) (c) Iron articles when come in contact with oxygen and water, to form rust, a flaky substance on its surface and slowly loses its strength. To avoid this it is painted frequently. (1) (d) Iron sheets are coated with zinc (galvanisation) so as to prevent iron from rusting.                                                                (1) (e) When copper vessels are exposed to moist air, (they form a green coating of basic copper carbonate The sour substances such as lemon or tamarind juice contain acids. These acids dissolve the coating of copper oxide or basic copper carbonate present on the surface of tarnished vessels and make them shining red-brown again.                                                    (1)