Lithium borohydride crystallizes in an orthorhombic system with4 molecule per unit cell. The unit cell dimensions are a=`6.8overset(@)A`, b `=4.4overset(@)A` and `c=7.2overset(@)A`. If the cell molar mass is 21.76 then the density of crystal is:

Options

A. `0.6708 g cm^(-3)`
B. `1.6708g cm^(-1)`
C. `2.6708 g cm^(-3)`
D. none of these

Explanation

(A) `n=4,M=21.76,av."no".=6.023xx10^(23)` and V `=axxbxxc=6.8xx10^(-8)xx4.4-10^(-8)xx7.2xx10^(-8)=2.154xx10^(-22)cm^(3)`
Density=`(nxx"mol wt.")/(Vxx"av.m")=(4xx21.76)/(2154xx10^(-22)xx6.023xx10^(23))=0.6708gcm^(-3)`