Explain why, the surface of some metals acquires a dull appearance when exposed to air for a long time.

(a) Which of the following metals would give hydrogen when added to dilute hydrochloride acid (i) iron (ii) copper (iii) magnesium ? (b) Explain why do surfaces of some metals acquire a dull appearance when exposed to air for a long time.

Why do some metals acquire a dull appearance on exposure to air for a long time ?

Explain why the surfaces of some metals become dull when exposed to air for sometime.

Give reasons for the following : (i) Carbonate and sulphide ores are converted into oxides before reduction. (ii) Aluminium is rendered passive when it is dipped in conc. HNO_(3) (iii) Nonmetals do not displace hydrogen from acids. (iv) An aqueous solution of CuSO_(4) cannot be stored in an iron vessel. (v) The surface of some metals become dull when left exposed to air for a long time.

Crystals of ferrous sulphate when exposed to air become

Alkali metals when exposed to air tranish quickly due to the