State two ways to prevent the rusting of iron.

Food cans are coated with tin and not with zinc because

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.

What chemical process is used for obtaining a metal from its oxide?

$(i)$ 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?

Give reasons: $Sodium$,$potassium$,and $lithium$ are stored under oil.