In the electrolysis of alumina using cryolite, the reaction that takes place at cathode is:

Which of the following metal oxide(s) gives metal and oxygen on heating ? 

The order the reactivity of some metals are given. Answer the following questions by analyzing it.
Al > Zn > Cu > Au
Metal ore which is reduced by carbon is

The extraction of metals from oxide ores involve(s) :

Explain with reasons:
Carbon can reduce lead oxide but not aluminium oxide.

The extraction of metals from oxide ores may involve:

The oxide of a metal (R) can be reduced by the metal (P) and metal (R) can reduce the oxide of metal (Q). Then the decreasing order of the reactivity of metal (P), (Q) and (R) with oxygen is :

Metal ions like $A{g}^{+},C{u}^{2+}$ etc. act as 

The main source of lead is $PbS$. It is converted to $Pb$ by the reactions are shown above. Out of these, the self-reduction process is: