Arrange the following according to the instructions given in bracket:

$\mathrm{K}, \mathrm{Pb}, \mathrm{Ca}, \mathrm{Zn}$. (In the increasing order of the reactivity)

Answer the following question based on the extraction of aluminium from alumina by Hall-Heroult’s Process.

What is the function of cryolite used along with alumina as the electrolyte? 

Answer the following question based on the extraction of aluminium from alumina by Hall-Heroult’s Process.

Why is powdered coke sprinkled on top of the electrolyte?

Answer the following question based on the extraction of aluminium from alumina by Hall-Heroult’s Process.

Name the electrode, from which aluminium is collected.

Name the gas evolved in the following case:

Alumina undergoes electrolytic reduction.

State one relevant observation for the following reactions:

• Sulphide ore is added to a tank containing oil and water and then stirred or agitated with air.

Give one word or a phrase for the following statement:

• Electrode used as a cathode in electrorefining of impure copper.

Name the following element:

• A monovalent non-metal present in fluorspar.