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2 mL each of conc. HCl, conc.HNO3 and a ...

2 mL each of conc. HCl, conc.`HNO3` and a mixture of conc.HCl and `HNO_3` 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 and B but the metal got dissolved in test tube C. the metal could be

A

Al

B

Au

C

Pt

D

Both (2) and (3)

Text Solution

AI Generated Solution

The correct Answer is:
To solve the question, we need to analyze the information provided about the reactions of metals with the different solutions in the test tubes. ### Step-by-Step Solution: 1. **Identify the Solutions in Test Tubes:** - Test Tube A: Contains 2 mL of concentrated HCl (Hydrochloric acid). - Test Tube B: Contains 2 mL of concentrated HNO3 (Nitric acid). - Test Tube C: Contains a mixture of concentrated HCl and HNO3 in a ratio of 3:1 (known as aqua regia). 2. **Understand the Behavior of Metals with Acids:** - Some metals react with acids to produce hydrogen gas and a salt. - However, not all metals react with HCl or HNO3. For instance, metals like gold (Au) and platinum (Pt) do not react with HCl or HNO3 alone. 3. **Analyze the Results:** - In Test Tubes A and B, no change occurred when the metal was placed in either solution. This indicates that the metal does not react with either concentrated HCl or concentrated HNO3. - In Test Tube C, the metal dissolved, indicating a reaction occurred. Since Test Tube C contains aqua regia, it can dissolve noble metals like gold and platinum. 4. **Determine the Possible Metals:** - Given that the metal dissolved only in Test Tube C (aqua regia), we can conclude that the metal must be one that is capable of reacting with this mixture. - The metals that can be dissolved in aqua regia include gold (Au) and platinum (Pt). 5. **Evaluate the Options:** - Option 1: Aluminium - Incorrect, as it would react with HCl. - Option 2: Gold (Au) - Correct, as it dissolves in aqua regia. - Option 3: Platinum (Pt) - Correct, as it also dissolves in aqua regia. - Option 4: Both 2 and 3 - Correct, as both gold and platinum can be dissolved in aqua regia. ### Conclusion: The metal could be either gold (Au) or platinum (Pt), or both. ### Final Answer: The metal could be gold (Au) or platinum (Pt), hence the correct option is both 2 and 3. ---
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