Predict the modes of occurrence of the following three types of metals :
(a) Highly reactive (e.g `Na`)
(b) Moderately reactive (e.g `Fe`)
( c) Noble metal (e.g `Au`).

Explanation

(i) Highly reactive : Being highly reactive in nature, it does not occur in nature in free state. In the combined form, sodium occurs as
(a) Sodium chloride, `NaCl`
(b) Sodium nitrate or Chile saltpetre, `NaNO_(3)`
( c) Sodium carbonate, `Na_(2) CO_(3)`
(d) Borax, `Na_(2) B_(4)O_(7).10 H_(2) O`.
(ii) Moderately reactive : Being moderately reactive in nature, it does not occur in nature in free state. In the combined form, iron occurs as
(a) Magnetic, `Fe_(3)O_(4)`
(b) Haematite, `Fe_(2)O_(3)`
( c) Limonite or hydrated ferric oxide, `Fe_(2)O_(3).3H_(2)O`
(d) Siderite or spathic iron, `FeCO_(3)`
( e) Iron pyrites, `FeS_(2)`
(f) Chalcopyrites, `CuFeS_(2)`.
(iii) Noble metal : Being noble metal, it is found in free state in nature, e.g. `Au,Pt` etc.