Capable of dissolving gold, ‘“aqua regia” is a mixture of hydrochloric and which other acid?

"Aqua regia", is a mixture of concentrated nitric (HNO3) and hydrochloric acids (HCI), usually one part of the former to three parts of the latter by volume. It was given its name (literally, “royal water”) by the alchemists because of its ability to dissolve gold and other so-called "noble" metals, though not all metals. "Aqua regia" was first mentioned in the works of Islamic alchemists such as Muhammad ibn Zakariya al-Razi (854-925), and then later mentioned in a work of Pseudo-Geber (ca. 1300)

"Aqua regia" and other mixtures similar to it are used in analytical procedures for the solution of certain iron ores, phosphate rocks, slags, nickel-chromium alloys, antimony, selenium, and some of the less soluble sulfides, such as those of mercury, arsenic, cobalt, and lead.

Due to the reaction between its components resulting in its decomposition, "aqua regia" quickly loses its effectiveness (yet remains a strong acid), so its components are usually only mixed immediately before use.

While local regulations may vary, "aqua regia" may be disposed of by careful neutralization, before being poured down the sink. If there is contamination by dissolved metals, the neutralized solution should be collected for disposal.