2 mL each of conc. HCl, cone. HNO3 and a mixture of conc. HCl and conc. HNO3 in the ratio of 3: 1 were taken in test tubes labelled as A, B, and C. A small piece of metal was put in each test tube. No change occurred in test tubes A But the metal got dissolved in test tube C. The metal could be.

1. Al
2. Au
3. Cu
4. Pt.

Correct Answer:  (b) Au

Explanation: Solution C is a mixture of Concentrated HCl and Concentrated HNO3 which is called aqua regia. Aqua Regia dissolves gold.