9th Class Science Atoms and Molecules Question Bank Atoms and Molecules

  • question_answer
    Selenium ingestion of \[90\] micrograms per day causes loss of hair. How many selenium atoms are there in this sample? (Atomic weight of \[Se=78.96\])

    A)  \[6.8\times {{10}^{23}}\]atoms

    B)         \[8.8\times {{10}^{17}}\]atoms

    C)  \[8.8\times {{10}^{22}}\]atoms

    D)         \[6.9\times {{10}^{17}}\]atoms  

    Correct Answer: D

    Solution :

     Atomic weight of\[Se=78.96\,\,g\] Number of moles in \[90\] micrograms             \[=\frac{90\times {{10}^{-6}}}{78.96}=1.139\times {{10}^{-6}}\]moles \[1\] mole of selemium atoms\[=6.023\times {{10}^{23}}\] \[1.139\times {{10}^{-6}}\]moles of selemium atoms\[=1.139\times {{10}^{-6}}\times 6.023\times {{10}^{23}}\]             \[=6.9\times {{10}^{17}}\]atoms


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