Hint: We know that Gold \[(Au)\] is a lustrous yellow piece of metal which belongs to group $11$ and period $6$ of the periodic table. The atomic number of gold is $79$ and hence it has an electronic configuration of $[Xe]4{f^{14}}5{d^{10}}6{s^1}$ . The chemical reactivity of gold is very low but it is a good conductor of heat and electricity.
Complete answer:As we know that gold is a less reactive metal so it can only be dissolved in Aqua regia.
Now Aqua regia is a yellow-orange or a red-orange fuming and a corrosive liquid which is made up of a mixture of hydrochloric acid $(HCl)$ and nitric acid $(HN{O_3})$ .This solution was first invented by Arab alchemist in the $8th$ century. It is also known as the royal water. It is given the name royal water as it has an ability to dissolve gold in it and gold is also known as the royal metal.
Aqua regia is prepared by combining one part of $conc.HN{O_3}$ to three parts of $HCl$ . hence the ratio of $HN{O_3}:HCl = 1:3$ .
Now let us see what happens when gold is dissolved in aqua regia: -
When we dissolve gold in aqua regia, an acid is formed which is known as the Chloroauric acid $(HAuC{l_4})$ .
So, we write the reaction as: -
$Au + HN{O_3} + 4HCl \to HAuC{l_4} + NO + 2{H_2}O$
Hence the Chloroauric acid is used in the process of electrolysis to purify gold.
Uses of Aqua regia: -
1. It can easily dissolve noble metals like gold and platinum but not all metals.
2. It is used in the manufacture of chloroauric acid.
3. It is also used as an electrolyte for refining gold by Wohlwill method
4. It is used in some laboratories to clean glassware.
Hence the chemical is Aqua regia.
Note:Gold dissolves in aqua regia as aqua regia consists of $conc.HN{O_3}$ which is a strong oxidizer. It oxidizes gold and forms $A{u^{ + 3}}$ ions and results in the removal of gold ions present in the solution. Also, the aqua regia solution is at room temperature and has a $pH$ of zero. In the early century, at the time of Adolf Hitler, aqua regia was used to hide the two gold Nobel medals from the Nazis.
