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The Solid State

Question 117
CBSEENCH12005465
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Explain Ionic solids are hard and brittle. 

Solution
 In ionic solids, constituent particles are held together with strong electrostatic force of attraction along with their fixed position. The fixed position of ions and strong electrostatic force of attraction make ionic solids hard and brittle.
Question 118
CBSEENCH12005466
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Give reasons for ZnO becomes yellow on heating.

Solution

Metal excess defect due to the presence of extra cations at interstitial sites: Zinc oxide is white in colour at room temperature. On heating it loses oxygen and turns yellow
Question 119
CBSEENCH12005467
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Give reasons for Solids with F-centres are paramagnetic?

Solution
f centres are the anionic vacancies occupied by unpaired electron. since the presence of unpaired electrons shows paramagnetic.
Question 120
CBSEENCH12005468
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Give reasons for Cation vacancies in some crystals make them good catalysts.

Solution
The catalytic activity dependsvery much on the surface area per unit mass of the sample.
Transition metal corresponds show metal deficiency due to absence of metal ion from its lattice. The charge is balanced by an adjacent ion having higher positive charge which ultimately increases chemisorption.

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