Give reasons: (i) "Alloys of iron are more useful when compared to pure iron."
(ii) Copper loses its brown layer gradually when exposed to air.
(iii) Aluminium oxide is called amphoteric oxide.

Explanation

(i) Pure iron is very soft.
Streches easily when hot
Alloys are hard.
The propertics of iron can be changed if it is mixed with other substances.
(ii) Copper reacts with moist carbon dioxide in the air and slowly loses its shiny brown surlace and gains a green coat.
(iii) Aluminium oxide `(Al_(2)O_(3))` reacts with both acids as well as bases to produce salt and water.