Question

Which reagent is able to dissolve gold and platinum?

• A. Nitric Acid
• B. Aqua-regia
• C. Hydrochloric acid
• D. Sulphuric acid

Answer 1

The correct option is B

Aqua-regia

An explanation for the correct option:

The correct option is B.

1. Aqua-regia is basically a mixture of Nitric acid $\left({\mathrm{HNO}}_3\right)$ and Hydrochloric acid $\left(\mathrm{HCl}\right)$ in a ratio of $1:3$.
2. Nitric acid and Hydrochloric acid react with each other and produce nitrosyl chloride, which is a strong oxidizing agent.
3. The presence of nitrosyl chloride in Aqua-regia is the reason that the Nobel metals are soluble in the Aqua-regia.
4. Gold, silver, and platinum are some Nobel metals.

An explanation for the incorrect options:

Option A:

1. Nitric acid produces two ions that are ${\mathrm{H}}^{+}\mathrm{and}{{\mathrm{NO}}_3}^{-}$.
2. Together they form a strong oxidizing agent but their strongness is not enough to dissolve gold and platinum.
3. Note that only Silver can dissolve in Nitric acid.

Options C and D:

1. The ${\mathrm{H}}^{+}$ ions produced by Hydrochloric acid and Sulphuric acid are not strong oxidizing agents; that's why Nobel metal cannot dissolve in these acids.

Final answer: Hence, option B is correct. Aqua-regia is reagent is able to dissolve gold and platinum.