Question

Which of the following is used for the dissolution of gold:
(A) Hydrochloric acid
(B) Sulphuric acid
(C) Nitric acid
(D) Aqua regia

Answer 1

Hint: Gold is dissolved in a mixture also known as royal water. This mixture is also used to dissolve metal like palladium, gallium and other noble metals.

Complete step by step solution:
Gold is a metal which is soft and mostly unreactive, this is the main reason why gold is used to make jewellery because it does not react when exposed to water, air etc. let’s talk about the reaction of gold in detail.
Gold metal is usually stable in air but it does dissolve in a solution of aqueous cyanide in the presence of air. It does not react with water.
Gold reacts with halogens and generally forms trihalides gold with chlorine and bromine however it forms monohalide gold when it reacts with iodine.
Aqua regia is also known as royal water and is used for the dissolution of gold. It is a mixture of hydrochloric acid and nitric acid present in the ratio of 3:1 or we can say that aqua regia is formed by mixing three parts of nitric acid and one part of hydrochloric acid. The name aqua regia was coined because this solution can dissolve gold which is known as the king of metals.
Nitric acid is a powerful oxidizer, it dissolves gold and forms $A{{u}^{3+}}$and hydrochloric acid provide chloride ion which reacts with gold and form$AuC{{l}_{4}}^{-}$.

Hence the correct option is (D).

Note: Formation of $AuC{{l}_{4}}^{-}$ anion helps in the removal of the gold ion from the given solution and after that the further oxidation of gold ions takes place. Chloroauric acid is produced by dissolution of gold.