State the role of 
(i) depressant in froth floatation process.
(ii) silica in the metallurgy of copper.
(iii) graphite rod in the electrolytic reduction of alumina.

The reaction:
\({ Cr }_{ 2 }{ O }_{ 3 }+2Al\rightarrow { Al }_{ 2 }{ O }_{ 3 }+2Cr;\ \triangle { G }^{ ° }=-421\quad kJ\) 
is thermodynamically feasible as is apparent from Gibbs energy value. Why does it not take place at room temperature?

Explain the role of
(i) cryolite in the electrolytic reduction of alumina.
(ii) carbon monoxide in the purification of nickel.

(i) Name the method of refining of metals such as germanium.
(ii) In the extraction of Al, impure \({ Al }_{ 2 }{ O }_{ 3 }\) is dissolved in conc. NaOH to form sodium aluminate and leaving impurities behind. What is the name of this process?
(iii) What is the role of coke in the extraction of iron from its oxides?

While washing a miner's overalls, a washer woman noticed that sand and similar dirt fell to the bottom of the wash tub. What was peculiar, the copper bearing compounds that had come to the clothes from the mines were caught in the soaplids and so they came to the top. One of her clients was a chemist, Mrs. Malik. The washer woman told her experience to Mrs. Malik. The latter thought that the idea could be used for separating copper compounds from rocky and earth materials on a large scale. After reading the above passage answer the following questions-
(i) Name the process of concentration of ore based on the observation of washer woman.
(ii) What type of ores are concentrated by this process?
(iii) What values are shown by washer woman and Mrs.Malik?

While washing a miner's overalls, a washer woman noticed that sand and similar dirt fell to the bottom of the wash tub. What was peculiar, the copper bearing compounds that had come to the clothes from the mines were caught in the soaplids and so they came to the top. One of her clients was a chemist, Mrs. Malik. The washer woman told her experience to Mrs. Malik. The latter thought that the idea could be used for separating copper compounds from rocky and earth materials on a large scale. After reading the above passage answer the following questions-
What values are shown by washer woman and Mrs.Malik?

In roasting, the are is heated in a regular supply of air in furnace at a temperature below the melting point of the metal. Metal sulphide gets converted into metal oxide and sulphur dioxide gas is formed
which is air pollutant. It also leads to the formation of acid rain which is harmful for crops and buildings made from marble.
How can sulphuric acid help in national economy?

Metals are very useful in our daily life. Aluminium powder is used in white paints. It is also used as a reducing agent. Alloys containing aluminium being light, are very useful. Utensils of aluminium are more popular than utensils of brass. Metals like silver, gold, iron, copper, zinc are very useful in our daily life.
Why are aluminium vessels preferred over copper and bronze vessels?

Metals are very useful in our daily life. Aluminium powder is used in white paints. It is also used as a reducing agent. Alloys containing aluminium being light, are very useful. Utensils of aluminium are more popular than utensils of brass. Metals like silver, gold, iron, copper, zinc are very useful in our daily life.
What value is associated for using aluminium?