Aqua regia is a corrosive, fuming, acidic mixture of concentrated hydrochloric acid and nitric acid that is used to dissolve noble metals like gold, platinum, and palladium

 Aqua regia is a corrosive, fuming, acidic mixture of concentrated hydrochloric acid and nitric acid that is used to dissolve noble metals like gold, platinum, and palladium: 

Composition

A 1:3 mixture of concentrated hydrochloric acid (HCl) and concentrated nitric acid (HNO3) 

Properties

A fuming liquid that is colorless when freshly prepared, but turns yellow, orange, or red within seconds

Uses

Removes noble metals from substrates, especially in microfabrications and microelectronics labs. It can also be used to wash glassware to remove trace amounts of organic compounds 

Safety

Extremely corrosive and can cause skin burns, eye irritation, respiratory tract irritation, and explosion. Always wear appropriate personal protective equipment (PPE) when handling aqua regia, including a lab coat, long pants, closed-toe shoes, and gloves compatible with nitric and hydrochloric acid. 

Here are some other things to know about aqua regia:

The Latin phrase aqua regia translates to "Royal Water" 

The boiling point of aqua regia is 108 °C, and its melting point is -42 °C

The density of aqua regia is 1.21 g/cm³

Nitrosyl chloride (NOCl) decomposes over time, producing chlorine gas and nitric oxide (NO) that auto-oxidizes to nitrogen dioxide (NO2), a poisonous reddish-brown gas