BCECE Engineering BCECE Engineering Solved Paper-2011

  • question_answer
    Given mass number of gold = 197, Density of gold \[=19.7\,g/c{{m}^{3}}\] Avogadros number \[=6\times {{10}^{23}}\]. The radius of the gold atom is approximately

    A)  \[1.5\times {{10}^{-8}}m\]         

    B)  \[1.7\times {{10}^{-9}}m\]

    C)  \[1.5\times {{10}^{-10}}m\]       

    D)        \[1.5\times {{10}^{-12}}m\]

    Correct Answer: C

    Solution :

    Volume occupied by one gram atom of gold \[=\frac{197g}{19.7\,g/{{m}^{3}}}=10\,c{{m}^{3}}\]          Volume of one atom\[=\frac{10}{6\times {{10}^{-23}}}\]                                                 \[=\frac{5}{3}\times {{10}^{23}}\,c{{m}^{3}}\]                    Let r be the radius of the atom \[\therefore \]  \[\frac{4}{3}\pi {{r}^{3}}=\frac{5}{3}\times {{10}^{23}}\] \[{{r}^{3}}=\frac{50\times {{10}^{-24}}}{4\times 3.14}\] \[r=1.5\times {{10}^{-10}}\,m\]


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