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# Chromium metal crystallizes with a b.c.c lattice. The edge length of the unit cell is found to be 287pm. Calculate the density of chromium in $g\;cm^{-3}$(at weight of cr = 52).

$(a)\;4\qquad(b)\;5\qquad(c)\;6\qquad(d)\;7$

Density $\rho = \large\frac{Z\times at . wt}{V\times Av.no.}$
$\;\;\;\;\;\;\;\;\;\;\;\;=\large\frac{Z\times at.wt.}{a^3\times Av.no.}$
Z = 2 for b.c.c a = 287
pm = $287\times10^{-10}cm$
$\rho = \large\frac{2\times52}{(287\times10^{-10})^3\times6.023\times10^{23}}$
$\;\;\;\; = 7.3$
$\;\;\;\;= 7g\;cm^{-3}$