Aqua regia is a mixture of concentrated HCl and concentrated HNO3  in the ratio ______.3 : 12 : 31 : 21 : 3

Break Down the Problem

1. Identify the components of aqua regia.
2. Determine the proper ratio of hydrochloric acid (HCl) to nitric acid (HNO₃).

Relevant Concepts

1. Aqua regia is a highly corrosive mixture used in gold dissolution, composed of concentrated hydrochloric acid and concentrated nitric acid.
2. The typical volume ratio of concentrated HCl to concentrated HNO₃ in aqua regia is approximately 3:1.

Analysis and Detail

1. The mixture is commonly prepared with three parts hydrochloric acid (HCl) to one part nitric acid (HNO₃).
2. Among the provided options (3 : 12 : 31 : 21 : 3), the only relevant ratio to the composition of aqua regia is 3:1.

Verify and Summarize

1. The standard formulation of aqua regia is confirmed as 3 parts HCl to 1 part HNO₃.
2. Ratios such as 12, 31, or 21 do not correspond to the standard composition ratio.

Final Answer

The correct ratio for aqua regia is 3:1 (or similarly stated as 3 parts HCl to 1 part HNO₃).