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The two requirements for vapour phase refining are: 

1. The metal should form a volatile compound with a suitable reagent. 

2. The volatile compound is decomposed to give the pure metal.

The anode (which is made of carbon) is attacked by nascent oxygen formed due to the discharge of O^2- ions and changes to carbon dioxide. As the anode is gradually consumed, it is periodically renewed. 

The compound is cryolite [Na₃AlF₆ ] 

The addition of cryolite lowers the melting point of alumina from 2050°C to 660 °C. 

Furthermore, it increases the electrical conductivity of the molten alumina. 

(d) In the metallurgy of gold, the metal is leached with dilute sodium chloride solution

A naturally occurring substance obtained by mining which contains the metal in free state or in the form of compounds like oxides, sulphides etc… is called as mineral. Bauxite and clay are minerals of Aluminium.

(d) Both (a) and (c)

Electrochemical principles also find applications in metallurgical process. The reduction of oxides of active metals such as sodium, potassium etc., by carbon is thermodynamically not feasible. Such metals are extracted from their ores by using electrochemical methods. In this technique, the metal salts are taken in a fused form or in solution form. The metal ion present can be reduced by treating it with some suitable reducing agent or by electrolysis. Gibbs free energy change for the electrolysis process is given by the following expression

∆G° = -nFE°

Where n is number of electrons involved in the reduction process, F is the Faraday and E° is the electrode potential of the redox couple. If E° is positive then the ∆G is negative and the reduction is spontaneous and hence a redox reaction is planned in such a way that the e.m.f of the net redox reaction is positive. When a more reactive metal is added to the solution containing the relatively less reactive metal ions, the more reactive metal will go into the solution.

For example,

Cu (s) + 2Ag⁺(s) → Cu²⁺(aq) + 2Ag (s)

Cu²⁺(aq) + Zn (s) → Cu (s) + Zn⁺(aq)

(a) Carbon reduction

(i) – (c) 

(ii) – (d) 

(iii) – (a) 

(iv) – (b)

Oxides are highly active metals like potassium, sodium, calcium, magnesium and aluminium have great affinity towards oxygen and so cannot be reduced by coke. 

(i) Duralumin, an alloy of aluminium, is used in the construction of aircraft; because it is light, resistant to corrosion and has great tensile strength. 

(ii) The rusting of iron is a process of atmospheric corrosion, i.e., slow destruction of iron by moisture and atmospheric oxygen. Rust is a reddish-brown powdery deposit and consists of a mixture of ferric hydroxide and hydrated ferric oxide. 

(iii) (a) (1) Nickel Plating and (2) Galvanizing. 

(b) By painting and by coating with nickel. 

(c) Iron coated with zinc is called galvanized iron. Galvanization is a process of depositing a thin layer of zinc, over the surface of iron to protect iron from rusting. Zinc is more electropositive and would be attacked first and thus iron is protected from any corrosion. Galvanized iron is used in making different varieties of tools for industries, scientific apparatus and household fittings. 

(d) Galvanisation. 

Alloys are classified on the basis of their constituents. They are classified as follows: 

(a) Ferrous alloys. 

(b) Amalgams. 

(c) Non-ferrous alloys. 

In moist air, a thin layer of aluminium oxide is formed on it quickly which protects aluminium to oxidise. This is the reason why aluminium does not oxidise rapidly in air.

Extraction of aluminium is difficult because : 

(i) Pure aluminium oxide melts at 2050°C only. So, a large amount of energy is needed to maintain this high temperature. 

(ii) A good amount of the aluminium vaporises at this temperature. 

(iii) Fused alumina does not conduct electricity well.

(i) The gas Y, carbon dioxide and the gas Z, is carbon monoxide. The gas Z is a reducing agent because it removes oxygen from iron oxide and converts it into metallic iron and itself gets oxidized to carbon dioxide. 

(ii) (a) Iron, Chromium, (b) Zinc

The thermite reaction in which iron oxide is reduced by aluminium. Aluminium is used as a reducing agent in the thermit reaction.

i. When old iron bars in the buildings are exposed to moist air for a long time, they acquire a coating of browm nlaky substance called rust. (Fe₂O₃.H₂O)

ii. If copper vessels are not cleaned for a long time, they react with moist carbon dioxide in the air, lose their shine and gain a green coat of copper carbonate. (CuCO₃)

When silver ornaments or idols are kept exposed to air for a long time, silver reacts with sulphur in the air to form a coating of black silver sulphide. (Ag₂S)