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Ionic solids, which have anionic vacancies due to metal excess defect, develop colour. Explain with the help of a suitale example.

When crystals of NaCl are heated in an atmosphre of sodium vapour, the sodium atoms are deposited on the surface of the crystal. The CI ions diffuse to the surface of the crystal and combine with Na atoms to give NaCl. This happens by loss electron by sodium atom to form Na+ ions. The released electrons diffuse into the crystals and occupy anionic sites. As a result the crystal now has an excess of sodium. They impart yellow colour to the crystals of NaCl.
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A group 14 element is to be converted into N-type semi-conductor by doping it with a suitable impurity. To which group should this impurity belong?

This impurity should belong to group 15.
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Explain how vacancies are introduced in an ionic solid when a cation of higher valence is added as an impurity in it.

If we mix a small amount of molten strontium chloride (SrCl2) with molten sodium chloride (NaCl) and the resulting solution is cooled, in the crystals of NaCl some Na+ ions will get replaced by Sr2+ ions. In order to maintain electron neutrality too Na+ ions are to leave their respective lattice sites. However, one out of them will be occupied by the Sr2+ion while the other will remain unoccupied or it will be vacant. Thus vacancies are introduced in an ionic solid.
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What type of substances would make better permanent magnets, ferromagnetic or ferrimagnetic, justify your answer.


Ferromagnetic substances would make better permanent magnets.In solid state, the metal ions of ferromagnetic substances are grouped together into small regions called domains. Thus, each domain acts as a tiny magnet. In an unmagnetised piece of a ferromagnetic substance the domains are randomly oriented and their magnetic moments get cancelled. When the substance is placed in a magnetic field all the domains get oriented in the direction of the magnetic field  and a strong magnetic effect is produced. This ordering of domains persist even when the magnetic field is removed and the ferromagnetic substance becomes a permanent magnet.
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What type of stoichiometric defect is shown by
(i) ZnS, (ii) AgBr (iii) KCl


(i) Frenkel defect.
(ii) Schottky defect and Frenkel defect.
(iii) Schottky defect.

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