The volume of colloidal particle ${\mathrm{V}}_{\mathrm{C}}$ as compared the volume of a solute particle in a true solution ${\mathrm{V}}_s$ to could be:

The ratio of volume is

$$\begin{gathered} \frac{{\mathrm{V}}_{\mathrm{c}}}{{\mathrm{V}}_{\mathrm{s}}}=\frac{\frac{4}{3}\pi {\mathrm{r}}_{\mathrm{c}}^3}{\frac{4}{3}{\mathrm{r}}_{\mathrm{s}}^3}=\frac{{\mathrm{r}}_{\mathrm{c}}^3}{{\mathrm{r}}_{\mathrm{s}}^3} \\ ={\left(\frac{10\times 2}{1\times 2}\right)}^3={10}^3 \end{gathered}$$

Diameter of solute particles$\simeq 10{\mathrm{A}}^{\circ }$

Diameter of true solution particle $\simeq 1{\mathrm{A}}^{\circ }$