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F-centre is...

F-centre is

A

anion vacancy occupied by unparired electron

B

anion vacancy occupied by electron

C

cation vacancy occupied by electron

D

anion present in iterstitial site

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The correct Answer is:
### Step-by-Step Solution: 1. **Understanding F-Centres**: - F-centres are a type of crystallographic defect found in ionic solids, particularly in alkali metal halides. - They are characterized by the presence of an anion vacancy in the crystal lattice. 2. **Definition of F-Centres**: - An F-centre specifically refers to an anion vacancy that is occupied by one or more unpaired electrons. This means that in the place where an anion (negative ion) is missing, there is an electron that is not paired with another electron. 3. **Properties of F-Centres**: - F-centres are known to impart characteristic colors to alkali metal halides. This is due to the presence of unpaired electrons which can absorb certain wavelengths of light. - Compounds with F-centres are paramagnetic, meaning they have unpaired electrons that contribute to their magnetic properties. 4. **Visual Representation**: - If we were to visualize an F-centre, we would depict a lattice structure where an anion site is vacant, and an unpaired electron is present in that vacancy. 5. **Choosing the Correct Option**: - Based on the definition and properties discussed, the correct answer to the question "F-centre is" can be summarized as: "Anion vacancies are occupied by unpaired electrons." ### Conclusion: - The correct option is **A**: Anion vacancies are occupied by unpaired electrons.
### Step-by-Step Solution: 1. **Understanding F-Centres**: - F-centres are a type of crystallographic defect found in ionic solids, particularly in alkali metal halides. - They are characterized by the presence of an anion vacancy in the crystal lattice. 2. **Definition of F-Centres**: - An F-centre specifically refers to an anion vacancy that is occupied by one or more unpaired electrons. This means that in the place where an anion (negative ion) is missing, there is an electron that is not paired with another electron. ...
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