Which method is used to obtain ultra-pure copper?

In the electrolytic purification of copper,some gold is found in the:

Formation of $Ni(CO)_4$ and its subsequent decomposition into $Ni$ and $CO$ (recycled) forms the basis of the Mond process.
$Ni + 4CO$ $\xrightarrow{T_1} Ni(CO)_4$ $\xrightarrow{T_2} Ni + 4CO$
$T_1$ and $T_2$ are:

Which of the following pairs of metals is purified by the van Arkel method?

$A$ metal which is refined by poling is

Explain chromatographic methods to refine the elements.