Aqua Regia ('Royal Water') is a highly corrosive mixture used to dissolve noble metals like Gold ($Au$) and Platinum ($Pt$) that are resistant to single acids.

• Composition: It is a mixture of approximately 3 parts concentrated $HCl$ and 1 part concentrated $HN{O}_3$ by volume.
• Reaction: The combination produces nascent Chlorine and Nitrosyl Chloride ($NOCl$):
• $3HCl+HN{O}_3\to NOCl+C{l}_2+2H_{2}O+[Cl]$
• The nascent chlorine reacts with Gold to form soluble Chloroauric acid ($HAuC{l}_4$).