Chapter 2 Atoms, Molecules, and Ions - Study Questions - Page 95: 3

$1\times10^{-13}\ cm$

Since the representation is proportional to the actual values, we can use the rule of three, where x is the actual nucleus diameter: $\dfrac{200\times10^2\ cm}{2\times10^{-1}\ cm}=\dfrac{1\times10^{-8}\ cm}{x}$ $x=1\times10^{-13}\ cm$