$KCl$ crystallizes in the same type of lattice as does $NaCl$.Givn that $\large\frac{r_{Na^+}}{r_{Cl^-}}$$=0.5$ and $\large\frac{r_{Na^+}}{r_{K^+}}$$=0.7$.Calculate the ratio of the side unit cell for $KCl$ to that for $NaCl$,and the ratio of density of $NaCl$ to that of $KCl$

Question

$\begin{array}{1 1}1.143,1.172\\2.143,2.172\\3.143,3.172\\4.143,4.172\end{array}$

Comments

why do we need consider 1.5 and 1.2