# NEET Chemistry The Solid State Questions Solved

Lithium borohydride $\left(LiB{H}_{4}\right),$crystallises in an orthorhombic system with 4 molecules per unit cell. The unit cell dimensions are : a = 6.81Å, b= 4.43Å, c=7.17Å. If the molar mass of $LiB{H}_{4}$ is 21.76 g mol–1. The density of the crystal is –

(1) 0.668 g cm–3

(2) 0.585 g cm2

(3) 1.23 g cm–3

(4) None

(1) We know that, $\rho =\frac{ZM}{{N}_{0}V}=\frac{4×\left(21.76\text{\hspace{0.17em}}gmo{l}^{-1}\right)}{\left(6.023×{10}^{23}mo{l}^{-1}\right)\text{\hspace{0.17em}}\left(6.81×4.43×7.17×{10}^{-24}c{m}^{3}\right)}$$=0.668\text{\hspace{0.17em}}g\text{\hspace{0.17em}}c{m}^{-3}$

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