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  5. The Solid State / ठोस प्रावस्था

12th Class Chemistry The Solid State / ठोस प्रावस्था Question Bank MCQs - The Solid State

  • question_answer
    What is the number of atoms per unit cell present in simple cubic, face-centered cubic and body centered cubic respectively?

    A) 4, 2, 1

    B) 2, 4, 1

    C) 4, 1, 2

    D) 1, 4, 2

    Correct Answer: D

    Solution :

    [d]
    In simple cubic unit cell, 8 atoms are present at its 8 corners. Each atom contributes one eighth per unit cell. So, total contribution \[=8\times \frac{1}{8}=1\]
    In fcc unit cell, 8 atoms are present at its 8 corners. Each atom contributes one eighth to the unit cell. So, total contribution \[=8\times \frac{1}{8}=1\]
    6 atoms are present at its 6 corners.
    Each atom contributes one half to the unit cell.
    Total contribution \[=6\times \frac{1}{2}=3\]
    \[\therefore \] Total number of atoms in fcc unit cell \[=1+3=4.\]
    In body unit cell, 8 atoms are present at its 8 corners.
    Each atom contributes one eighth to the unit cell.
    Total contribution \[=8\times \frac{1}{8}=1\]
    1 atom is present at body centre of bcc unit cell.
    The atom contributes fully to the unit cell.
    Total contribution \[=1\times \frac{1}{1}=1\]
    \[\therefore \] Total number of atoms in bcc unit cell \[=1+1=2\]


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