Q14 / 160 · AP EAMCET 2011 · Chemistry

The number of unit cells present in $39 \mathrm{~g}$ of potassium if it crystallizes as body centred cube is ( $N=$ Avogadro number, At. wt. of potassium $=39$ )

  • A
    $\frac{N}{4}$
  • Correct answer
    B
    $\frac{N}{2}$
  • C
    $\frac{N}{3}$
  • D
    $N$

Solution

Potassium has bcc system Number of mole $=39 / 39=1$ mole 1 mole of atoms $=6.022 \times 10^{23}$ atoms $=N$ $\because$ In bcc system 2 atoms are present in 1 unit cell. $\therefore N$ number of atoms are present in $\frac{N}{2}$ unit cells.

Hence, the correct answer is option: 'B'.

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