Colloid is a heterogeneous mixture in which the minute particles of a particular substance are dispersed into another substance, which is called the dispersion medium.
The minute particles have a diameter of 1 to 1000 nanometers but they still do not settle at the bottom of the mixture instead they remain suspended.
Thye can be seen under an electron or optical microscope.
Hence it is the correct option.
Therefore, The size of colloidal particles ranges between option (C)