KVPY Sample Paper KVPY Stream-SX Model Paper-1

  • question_answer
    Caesium broxide has CsCl structure (bcc lattice). Its density is 4.49 g \[c{{m}^{-3}}\]. The side of the unit cell is closest to

    A) 5.584 \[\overset{\text{o}}{\mathop{\text{A}}}\,\]            

    B) 4.285 \[\overset{\text{o}}{\mathop{\text{A}}}\,\]

    C) 47.392 \[\overset{\text{o}}{\mathop{\text{A}}}\,\]                      

    D) 1.121 \[\overset{\text{o}}{\mathop{\text{A}}}\,\]

    Correct Answer: B

    Solution :

    [b]
    Molar mass of \[CsBr\]
    \[=212.8g\,mo{{l}^{-\,1}}\]
    \[\therefore \]\[\text{Molar}\,\text{volume=}\frac{\text{molar}\,\text{mass}}{\text{density}}\]
    \[=\frac{212.8}{4.49}=47.39\,c{{m}^{3}}\]
    \[6.023\times {{10}^{23}}\]molecules are there in \[47.39\,c{{m}^{3}}\]
    1 molecule is there in\[\frac{47.39}{6.023\times {{10}^{23}}}\]
    \[=7.868\times {{10}^{-\,23}}c{{m}^{3}}\]
    \[\therefore \]Volume of the unit cell
    \[={{a}^{3}}=7.868\times {{10}^{-\,23}}c{{m}^{3}}\]
    Side of the unit cell
    \[=a={{(7.868\times {{10}^{-\,23}})}^{1/3}}\]
    \[=4.285\times {{10}^{-\,8}}cm\]
    \[=4.285\overset{{}^\circ }{\mathop{A}}\,\]


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