In the electrolytic refining of a metal $M$,what would you take as the anode,the cathode,and the electrolyte?

$(i)$ Write the electron-dot structures for sodium,oxygen,and magnesium.
$(ii)$ Show the formation of $Na_{2}O$ and $MgO$ by the transfer of electrons.
$(iii)$ What are the ions present in these compounds?

Why do ionic compounds have high melting points?

What are alloys?

Name two metals which will displace hydrogen from dilute acids,and two metals which will not.

Samples of four metals $A$,$B$,$C$ and $D$ were taken and added to the following solutions one by one. The results obtained have been tabulated as follows.

Metal	Iron $(II)$ sulphate	Copper $(II)$ sulphate	Zinc sulphate	Silver nitrate
$A$	No reaction	Displacement	No reaction	Displacement
$B$	Displacement	Displacement	No reaction	Displacement
$C$	No reaction	No reaction	No reaction	Displacement
$D$	No reaction	No reaction	No reaction	No reaction

Use the table above to answer the following questions about metals $A$,$B$,$C$ and $D$:
$(i)$ Which is the most reactive metal?
$(ii)$ What would you observe if $B$ is added to a solution of Copper $(II)$ sulphate?
$(iii)$ Arrange the metals $A$,$B$,$C$ and $D$ in the order of decreasing reactivity.