(i) The process in which no external reducing. When ore is heated in air, a part of the ore gets oxidised which combines with remaining sulphide to give metal.
Eg: Reduction copper glance (Cu₂S)
\({ 2Cu }_{ 2 }S+{ 3O }_{ 2 }\longrightarrow { 2Cu }_{ 2 }O+2{ SO }_{ 2 }\uparrow \)
\({ 2Cu }_{ 2 }O+{ Cu }_{ 2 }S\longrightarrow 6Cu+{ SO }_{ 2 }\uparrow \)
(ii) Electrolytic reduction is used for highly electro positive metals. In this method, fused metal ore is electrolysed and pure metal is deposited at cathode.
Eg: Al is obtained by electrolysis of Al₂O_{3
\({ 2Al }_{ 2 }{ O }_{ 3 }+3C\longrightarrow \underset { Cathode\quad Anode }{ 4Al+{ 3CO }_{ 2 } } \)}
(iii) \({ Cr }_{ 2 }{ O }_{ 3 }+2Al\longrightarrow {Al }_{ 2 }{ O }_{ 3 }+2Cr\)
\(3 \mathrm{Mn} _3 O_{4}+8 \mathrm{Al} \longrightarrow 4 \mathrm{Al}_{2} \mathrm{O}_{3}+9 \mathrm{Mn}\)

(i) Alumina is separated from silica in a bauxite ore through Baeyer's process, in which bauxite ore is concentrated by the method of leaching or chemical separation.
(ii) Chemical method is employed in case where the ore is to be in a very pure form, e.g., aluminium extraction. Bauxite (Al₂O₃), an ore of aluminium, contains SiO₂ and Fe₂O₃ as impurities. When bauxite ore is treated with NaOH, the Al₂O₃ goes into solution as sodium meta aluminate leaving behind the undissolved impurities [Fe₂O₃, SiO₂, Fe(OH)_3' etc.], which are then filtered off.
\({ Al }_{ 2 }{ O }_{ 3 }+{ 2NaOH }\longrightarrow \underset { Sod.meta.aliminate\\ (In \ solution \ form) }{ { 2NaAlO }_{ 2 }+{ H }_{ 2 }O } \)
(iii) The filtrate (containing sodium meta aluminate) on dilution, and stirring gives a precipitate of aluminium hydroxide, which is filtered, and ignited to get pure alumina.
\({ NaAlO }_{ 2 }+2{ H }_{ 2 }O\longrightarrow \underset { Ppt }{ { Al(OH) }_{ 3 } } +NaOH\)
\(2Al\left( OH \right) _{ 3 }\overset { \Delta }{ \longrightarrow } \underset { Pure }{ { Al }_{ 2 }{ O }_{ 3 } } +3{ H }_{ 2 }O\)

(i) Many heat exchangers/sinks and our day to day cooking vessels are made of aluminum.
(ii) It is used as wraps (aluminum foils) and is used in packing materials for food items.
(iii) Aluminum alloys with copper, manganese, magnesium and silicon are light weight and strong and they are used in design of aeroplanes and other forms of transport.
(iv) Aluminum shows high resistance, to corrosion, so it is used in the design of chemical reactors, medical equipments, refrigeration units and gas pipelines.
(v) Aluminium is a good electrical conductor and cheap, hence used in electrical overhead electric cables with steel core for strength.

(i) The impure nickel is heated in a stream of carbon monoxide at around 350 K.
(ii) The nickel reacts with the CO to form a highly volatile nickel tetracarbonyl.
(iii) The solid impurities are left behind 
\({ Ni }_{ (s) }+4{ CO }_{ (g) }\longrightarrow { Ni(CO) }_{ 4(g) }\)
(iv) On heating the nickel tetracarbonyl around 460 K, the complex decomposes to give pure metal.
\({ Ni(CO) }_{ 4(g) }\longrightarrow { Ni }_{ (s) }+{ 4CO }_{ (g) }\)

(i) Magnetic separation is applicable to ferromagnetic ores and it is based on the difference in the magnetic properties of the ore and the impurities.
(ii) For example tin stone can be separated from the wolframite impurities which is magnetic.
(iii) Similarly, ores such as chromite, pyrolusite having magnetic property can be removed from the non magnetic siliceous impurities.
(iv) The crushed ore is poured on to an electromagnetic separator consisting of a belt moving over two rollers of which one is magnetic.
(v) The magnetic part of the ore is attracted towards the magnet and falls as a heap close to the magnetic region while the nonmagnetic part falls away from it as shown in the figure.