Lithium borohydride crystallizes in an orthormobic system with 4 molecules per unit cell. The unit cell dimensions are `a =6.8 Å, b =4.4 Å` and `c= 7.2 Å`. If the molar mass is 21.76, then the density of crystals is:

Options

A. `0.6708 g cm^(-2)`
B. `1.6708 g cm^(-3)`
C. `2.6708 g cm^(-3)`
D. None of these

Answer

A

Explanation

`d = (ZM)/(a_(3)N_(A)) = (4 xx 21.76)/(6.8 xx 10^(-8) xx 4.4 xx 10^(-8) xx 7.2 xx 10^(-8) xx 6.023 xx 10^(23)) = 0.6708 g cm^(2-)`