NCERT Class XII Chemistry
Chapter - The Solid State
Questions with Solutions

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Question : 4
Total: 50
(i) What is meant by the term ‘coordination number’?
(ii) What is the coordination number of atoms :
(a) in a cubic close-packed structure?
(b) in a body-centred cubic structure?
Solution:  
(i) Coordination number is defined as the number of nearest neighbours in a close packing. In ionic crystals, coordination number of an ion in the crystal is the number of oppositely charged ions surrounding that particular ion.
(ii) (a) Coordination number of atoms in a cubic close- packed structure is 12.
(b) Coordination number of atoms in a body-centred cubic structure is 8.
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