Qualitative analysis of organic compounds is performed by Lassaigne's test by fusion with metallic sodium, by which the covalent compounds are converted into ionic compounds. Extra elementsline `N,S,P` andhalogensaredetected by their usual tests.
Q. Which of the following will give blood-red colour in lassaigne's test for nitrogen

Options

A. `PhNH_2`
B. `PhNO_2`
C.
D. `PhSO_3H`

Explanation

To solve the question regarding which compound will give a blood-red color in Lassaigne's test for nitrogen, we will follow these steps:

### Step 1: Understand Lassaigne's Test
Lassaigne's test is used to detect the presence of certain elements in organic compounds, specifically nitrogen (N), sulfur (S), phosphorus (P), and halogens. The organic compound is fused with metallic sodium, which converts covalent compounds into ionic compounds.

**Hint:** Remember that Lassaigne's test is primarily for detecting elements like N, S, P, and halogens.

### Step 2: Identify the Color Indication
In Lassaigne's test, a blood-red color indicates the presence of nitrogen when sulfur is also present in the compound. Therefore, for a compound to give a blood-red color, it must contain nitrogen, sulfur, and carbon.

**Hint:** Blood-red color in Lassaigne's test is specifically linked to the presence of nitrogen and sulfur.

### Step 3: Analyze the Given Options
We need to evaluate each option to see if it contains nitrogen, sulfur, and carbon.

1. **Option 1: Phenyl NH2 (C6H5NH2)**
- Contains carbon (C) and nitrogen (N).
- Does not contain sulfur (S).
- **Conclusion:** Will not give blood-red color.

2. **Option 2: C6H5NO2**
- Contains carbon (C) and nitrogen (N).
- Does not contain sulfur (S).
- **Conclusion:** Will not give blood-red color.

3. **Option 3: C6H4(NO2)SO3H**
- Contains carbon (C), nitrogen (N), and sulfur (S).
- **Conclusion:** Will give blood-red color.

4. **Option 4: C2H2S**
- Contains carbon (C) and sulfur (S).
- Does not contain nitrogen (N).
- **Conclusion:** Will not give blood-red color.

### Step 4: Final Conclusion
Based on the analysis, only **Option 3 (C6H4(NO2)SO3H)** contains nitrogen, sulfur, and carbon, and thus will give a blood-red color in Lassaigne's test.

**Final Answer:** Option 3 is the correct answer.

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