A mixture of sulphur and iron filings is heated strongly to obtain a residue. Which of the following is not a characteristic property of the residue?

Options

A. It can be separated into sulphur and iron filings by physical methods.
B. Its composition does not change from one part to another.
C. Its properties are entirely different from those of sulphur and iron filings.
D. Its appearance is different from those of sulphur and iron filings.

Explanation

To solve the question regarding the mixture of sulfur and iron filings that is heated to obtain a residue, we need to analyze the properties of the resulting compound, iron sulfide (FeS), and determine which statement is not a characteristic property of the residue.

### Step-by-Step Solution:

1. **Understanding the Reaction**: When sulfur and iron filings are heated together, they react to form iron sulfide (FeS). This is a chemical change where the original substances lose their individual properties and form a new compound.

2. **Identifying the Properties of Iron Sulfide (FeS)**:
- **Composition**: The composition of iron sulfide is fixed; it consists of one iron atom (Fe) and one sulfur atom (S). This means that the ratio of iron to sulfur does not change.
- **Separation**: Iron sulfide is a compound, which cannot be separated into iron and sulfur by physical methods. It requires a chemical reaction to break it down into its constituent elements.
- **Properties**: The properties of iron sulfide are different from those of its constituent elements (sulfur and iron). For example, iron sulfide is not magnetic, whereas iron filings are magnetic.
- **Appearance**: Iron sulfide has a distinct appearance (black color), which is different from the pale yellow color of sulfur and the silvery gray of iron filings.

3. **Analyzing the Options**:
- **Option A**: "It can be separated into sulfur and iron by physical method." - This is incorrect because iron sulfide cannot be separated by physical means; it requires a chemical process.
- **Option B**: "Its composition does not change from one part to another." - This is correct; the composition of FeS is uniform throughout.
- **Option C**: "Its properties are entirely different from those of sulfur and iron filings." - This is also correct; the properties of FeS differ from those of sulfur and iron.
- **Option D**: "Its appearance is different from those of sulfur and iron filings." - This statement is correct as well; FeS has a different color compared to sulfur and iron filings.

4. **Conclusion**: The statement that is not a characteristic property of the residue (iron sulfide) is **Option A**: "It can be separated into sulfur and iron by physical method."

### Final Answer:
**Option A** is not a characteristic property of the residue.

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