How to solve this question???

Dear student
CsCl has bcc arrangement, and Z =1, hence volume occupied effectively= mass of 1 CsCl / density
=$\frac{168}{3.988\times 6.022\times {10}^{23}}$=$7\times {10}^{-23}c{m}^3$
( mass of 1 mole of CsCl =168, mass of 1 molecule of CsCl= 168/avogadro number

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