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KVPY Sample Paper KVPY Stream-SX Model Paper-6

  • question_answer
    The radii of \[N{{a}^{+}}\] and \[C{{l}^{-}}\] ions are 95 pm and 181 pm respectively The edge length of \[NaCl\] unit cell is

    A) \[276pm\]                     

    B) \[138pm\]

    C) \[552pm\]                     

    D) \[415pm\]

    Correct Answer: C

    Solution :

    in a fcc lattice, the distance between the cation and anion is equal to the sum of their radii, which is equal to half of the edge length of unit cell,
    \[i.e.{{r}^{+}}+{{r}^{-}}=\frac{a}{2}\]       (where a=edge length)
    \[{{r}^{+}}=95pm,{{r}^{-}}=181pm\]
    \[Edge\text{ }length\text{ }=2{{r}^{+}}+2{{r}^{-}}=(2\times 95+2\times 181)\]
    \[pm=(190+362)pm=552pm.\]


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