Aqua regia is used for dissolving noble metals (Au, Pt, etc.). The gas evolved in this process is :

Options

A. `N_(2)O_(3)`
B. `N_(2)`
C. `N_(2)O_(5)`
D. `NO`

Explanation

To solve the question regarding the gas evolved when noble metals (like Au and Pt) are dissolved in aqua regia, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Aqua Regia**: Aqua regia is a mixture of hydrochloric acid (HCl) and nitric acid (HNO3) in a ratio of 3:1. It is known for its ability to dissolve noble metals such as gold (Au) and platinum (Pt).

2. **Chemical Reaction**: When noble metals are treated with aqua regia, they undergo a chemical reaction. For example, when gold (Au) reacts with aqua regia, the reaction can be represented as:
\[ \text{Au} + \text{HNO}_3 + \text{HCl} \rightarrow \text{HAuCl}_4 + \text{NO} + \text{H}_2\text{O} \]
Here, HAuCl4 is the gold chloride complex formed, and nitric oxide (NO) gas is evolved.

3. **Gas Evolution**: The gas that is produced in this reaction is nitric oxide (NO), which is a colorless gas. This is consistent for both gold and platinum when reacted with aqua regia.

4. **Conclusion**: Therefore, the gas evolved when noble metals are dissolved in aqua regia is nitric oxide (NO).

### Final Answer:
The gas evolved in the process of dissolving noble metals in aqua regia is **nitric oxide (NO)**.

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