Aqua regia used by alchemists to separate silver and gold is a mixture of

Aqua regia, historically known as 'royal water', is a highly corrosive and fuming liquid used by alchemists to dissolve noble metals like gold and platinum [1]. It is prepared by mixing concentrated hydrochloric acid (HCl) and concentrated nitric acid (HNO3) in a volume ratio of 3:1 [1]. While neither acid can dissolve gold individually, their combination produces reactive species like nitrosyl chloride and nascent chlorine, which facilitate the dissolution process. Silver is generally not dissolved by aqua regia because it forms an insoluble silver chloride (AgCl) layer that prevents further reaction, allowing for the separation of gold from silver. The mixture must be freshly prepared as it quickly loses its potency due to the decomposition into volatile gases.

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 3: Metals and Non-metals > p. 44