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Question
Assertion :Solids containing F-centres are paramagnetic. Reason: F-centres solids possess holes occupied by unpaired electrons.
Assertion :Solids containing F-centres are paramagnetic. Reason: F-centres solids possess holes occupied by unpaired electrons.
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Solution
The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
When potassium chloride is heated in sodium vapour, we see that it acquires a yellow colour. The heating in excess sodium creates new lattice sites for sodium. To maintain the structure, an equal number of chloride sites are also created but the latter are vacant. The electron of the potassium atom that is ionized in the KCl matrix is trapped by the chloride ion vacancy. This trapped electron can be freed into the crystal by absorbing visible light and hence, the colour. A trapped electron at an anion vacancy is an electronic defect and it is known as F-centre (from German Farbe meaning colour).
When potassium chloride is heated in sodium vapour, we see that it acquires a yellow colour. The heating in excess sodium creates new lattice sites for sodium. To maintain the structure, an equal number of chloride sites are also created but the latter are vacant. The electron of the potassium atom that is ionized in the KCl matrix is trapped by the chloride ion vacancy. This trapped electron can be freed into the crystal by absorbing visible light and hence, the colour. A trapped electron at an anion vacancy is an electronic defect and it is known as F-centre (from German Farbe meaning colour).
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