Which kind of impurities are present in the ores? What are these impurities collectively known as?

Which process is used to obtain metal from metal oxide?

$(a)$ Carbon cannot be used as a reducing agent to obtain $Mg$ from $MgO$. Why?
$(b)$ How is sodium obtained from molten sodium chloride? Give the equations of the reactions.
$(c)$ How is copper obtained from its sulphide ore? Give the equations of the reactions.

What is the typical carat value of gold used in jewelry?

An electrolytic cell consists of
$(i)$ positively charged cathode
$(ii)$ negatively charged anode
$(iii)$ positively charged anode
$(iv)$ negatively charged cathode

During the extraction of metals,electrolytic refining is used to obtain pure metals.
$(a)$ Which material will be used as the anode and cathode for the refining of silver metal by this process?
$(b)$ Suggest a suitable electrolyte as well.
$(c)$ In this electrolytic cell,where do we get pure silver after passing an electric current?