In the $Hall-Heroult$ process,which substances are added to alumina to lower its melting point?

In the $Bayer$ process,what is obtained when concentrated $NaOH$ is added to bauxite?

Four groups are given linking a metal, its ore, and the chemical formula of the main component of the ore. How many of these are correct?
$(1)$ Iron - Magnetite - $Fe_{3}O_{4}$
$(2)$ Iron - Siderite - $FeS_{2}$
$(3)$ Copper - Copper glance - $Cu_{2}S$
$(4)$ Copper - Dolomite - $Al_{2}O_{3}$

What is the percentage concentration of sodium hydroxide solution used in the Bayer process (in $\%$)?

Name two metals which are purified by electrolytic refining. Mention the anode,cathode and the electrolyte used in the refining process. At which electrode would the pure metal be deposited?

By which method is aluminum metal obtained by the reduction of alumina?