On the basis of reactivity metals are grouped into three categories - (i) Metals of low reactivity (ii) Metals of medium reactivity (iii) Metals of high reactivity. Therefore metals are extracted in pure form from their ores on the basis of their chemical properties. Metals of high reactivity are extracted from their ores by electrolysis of the molten ore. Metals of low reactivity are extracted from their sulphide ores, which are converted into their oxides. The oxides of these metals are reduced to metals by simple heating.

(a) Name the process of reduction used for a metal that gives vigorous reaction with air and water both.

(b) Carbon cannot be used as a reducing agent to obtain aluminium from its oxide? Why?

(c) Describe briefly the method to obtain mercury from cinnabar. Write the chemical equation for the reactions involved in the process.

OR

(c) Differentiate between roasting and calcination giving chemical equation for each.

The process of reduction used for a metal that gives vigorous reaction with air and water both is electrolysis. This is because metals that react vigorously with air and water are highly reactive and cannot be reduced by simple heating or using carbon as a reducing agent. Electrolysis is the process of using an electric current to drive a chemical reaction, and it is often used to extract highly reactive metals from their ores.

Carbon cannot be used as a reducing agent to obtain aluminium from its oxide because aluminium is more reactive than carbon. In order to reduce aluminium oxide to aluminium, a more reactive metal such as sodium or potassium is needed, or electrolysis must be used.

Mercury is obtained from cinnabar (mercury sulphide) through the process of roasting, followed by reduction. The chemical equation for the reaction involved in the process is:

2HgS + 3O2 $\rightarrow$ 2HgO + 2SO2

2HgO $\rightarrow$ 2Hg + O2

In the first equation, cinnabar is roasted in the presence of oxygen to produce mercury oxide and sulphur dioxide. In the second equation, the mercury oxide is reduced to mercury through simple heating.

OR

Roasting and calcination are two different processes used to convert ores into their oxides. Roasting is the process of heating an ore in the presence of air to convert it into its oxide, while calcination is the process of heating an ore in the absence of air to convert it into its oxide. The chemical equation for roasting is:

2ZnS + 3O2 $\rightarrow$ 2ZnO + 2SO2

The chemical equation for calcination is:

CaCO3 $\rightarrow$ CaO + CO2