Question

    How many sodium ions and chloride ions are present in a

    unit cell of sodium chloride crystal?  
    A 2 Correct Answer Incorrect Answer
    B 6 Correct Answer Incorrect Answer
    C 4 Correct Answer Incorrect Answer
    D 8 Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    (i) For a crystal of sodium the type if lattice in which it crystallises is Face Centered Cubic (fcc). (ii) The co-ordination number of each sodium ion and chloride ion in the crystal lattice is  6:6. (iii) The number of sodium ions and chloride ions present in a unit cell is 4 each. (iv) The structural arrangement of the sodium chloride crystal is cubic close packing with Cl− ions at corners and face centres and Na+ ions at edge centres and body centre, With respect to Na+ ion it is octahedral.

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