Chemistry Question on The solid state

Question

$AB$ crystallizes in a body centred cubic lattice with edge length 'a' equal to $387 \,pm$ . The distance between two oppositely charged ions in the lattices is

Answer 1

Solution

For $BCC$ lattice body diagonal $= a \sqrt{ 3}$ .
The distance between the two oppositely charged ions $= \frac{a}{2} \sqrt{3}$
$= \frac{387 \times 1.732}{2} = 335\, pm$