Specific number of particles per mL cannot be provided, but as a rough estimate, given that it's a 10% solution, can calculate based on 0.5 mL of particles. The average particle radius is 4 microns, resulting in an average particle volume of 268.08 um^3, or approximately 2.68e-10 cm3 (or mL). By dividing 0.5 mL by 2.68e-10, we obtain approximately 1.87e+9 particles. This calculation is based on 10% of the 5 mL solution being particles. It's important to note that this is a very rough estimation and should not be used for analytical purposes.
Please be aware that this estimate is not guaranteed, as even a slight deviation from the 4 micron radius could significantly alter the number of particles.