Question

The density of a pure substance ‘A’, whose atoms are arranged in a cubic close pack arrangement, is $1\text{g/cc}$. If all the tetrahedral voids are now filled with ‘B’ atoms, what is the density of the resulting solid in $\text{g/cc}$? [Molar mass $A=30\text{g/mol}$ and Molar mass $\text{B = 50 g/mol}]$

• A. 3.33
• B. 4.33
• C. 2.33
• D. 5.33

Answer 1

The correct option is B 4.33

We know that density can be given by:
$\rho =\frac{nM}{V{N}_A}$
For pure A, $1=\frac{4\times 30}{V{N}_A}$
$⟹V=\frac{120}{N_A}$
$\rho =\frac{4\times 30+8\times 50}{120}$
$⟹\rho =4.33g/cc$