Disodium pentacyanonitrosyl ferrate reagent gives purple colour when which of the following element is present.

Options

A. `N`
B. `Cl`
C. `F`
D. `S`

Answer

To solve the question regarding the disodium pentacyanonitrosyl ferrate reagent and the element that causes a purple color, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Reagent**: The reagent in question is disodium pentacyanonitrosyl ferrate, which can be represented as Na2[Fe(CN)5(NO)].

2. **Identify the Color Change**: The question asks which element, when present, causes the reagent to give a purple color.

3. **Consider the Options**: The options provided are nitrogen, chlorine, chlorine, and sulfur. We need to determine which of these elements interacts with the reagent to produce the purple color.

4. **Recall the Test**: The purple color is associated with a specific test known as the lacing test. This test is used to detect the presence of sulfur.

5. **Chemical Reaction**: In the presence of sulfur, sodium reacts to form sodium sulfide (Na2S). The sodium sulfide then reacts with the disodium pentacyanonitrosyl ferrate to form a new compound, Na4[Fe(CN)5NOS], which is purple in color.

6. **Conclusion**: Based on the above steps, we conclude that the element that causes the disodium pentacyanonitrosyl ferrate reagent to give a purple color is sulfur.

### Final Answer:
The answer is **sulfur**.

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