$\text{KCl}$ crystallises in the same type of lattice as $\text{NaCl}$. Calculate the ratio of the side of the unit cell for $\text{KCl}$ to that of $\text{NaCl}$.
(given ${\text{r}}_{{\text{Na}}^{\text{+}}}{\text{/r}}_{{\text{Cl}}^{\text{-}}}{\text{= 0.55 and r}}_{{\text{K}}^{\text{+}}}{\text{/r}}_{{\text{Cl}}^{\text{-}}}\text{= 0.74}$)