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# potassium crystallizes in a bode centred cubic lattice .What is the approximate number unit cells in 4.0 g of potassium ? Atomic mass of potassium =39.

$(a)\;3.09 \times 10^{22}\qquad(b)\;3.09 \times 10^{2}\qquad(c)\;2.05 \times 10^{22}\qquad(d)\;1.09 \times 10^{22}$

Answer : $3.09 \times 10^{22}$
No of atoms per unit $=8 \times \large\frac{1}{8}+\normalsize 1=2$
No of atoms is 4.0 g of potassium $\;=\large\frac{4}{39} \times \normalsize 6.023 \times \normalsize10^{23}$
No of unit cells in 4.0 g of potassium $\;=\large\frac{4}{39} \times \large\frac{6.023 \times 10^{23}}{2}$= $3.09 \times 10^{22}$