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In a BCC lattice with lattice constant 'a', the body-centered position from the origin is at a distance of :

  • A.\(\sqrt{2a}\)
  • B.\(\sqrt{\left(\frac{3}{2}\right)}a\)
  • C.\(\frac{\sqrt{3}}{2}a\)
  • D.\(\frac{\sqrt{3}}{4}a\)

Answer: C

The distance is \(\frac{\sqrt{3}}{2}a\).

The body centre of a cubic cell of side \(a\) is at \((a/2, a/2, a/2)\) from the corner taken as origin:

\[ \begin{aligned} d &= \sqrt{\left(\tfrac{a}{2}\right)^{2} \times 3} \\ &= \frac{\sqrt{3}}{2}a \end{aligned} \]

This is half the body diagonal \(\sqrt{3}a\), and it is the nearest-neighbour distance in BCC. \(\frac{\sqrt{3}}{4}a\) is the atomic radius (half that distance). \(\sqrt{2a}\) and \(\sqrt{3/2}\,a\) do not correspond to this point.

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