MCQ Detailed View

Colloids represent a unique state of matter that lies between true solutions and suspensions. The defining feature of a colloid is the size of its dispersed particles, which typically range from 1 nanometer (nm) to 1000 nanometers (1 micrometer). This size range is crucial in distinguishing colloids from other types of mixtures.

In a true solution (such as salt dissolved in water), the solute particles are very small, usually less than 1 nm. These particles are at the molecular or ionic level, making them invisible even under an ultramicroscope. True solutions are homogeneous and particles do not scatter light, which is why they show no Tyndall effect.

In contrast, suspensions (such as sand in water) contain much larger particles, usually greater than 1000 nm. These particles are visible to the naked eye, and they tend to settle down over time due to gravity. Suspensions are heterogeneous and can be easily separated by filtration.

Colloids fall in between these two extremes. Their particle size is larger than that of true solutions but smaller than that of suspensions. Because of this intermediate size, colloidal particles are not visible under an ordinary microscope but can be detected under an ultramicroscope. Colloids also exhibit special properties such as the Tyndall effect (scattering of light), Brownian motion (random movement of particles), and relative stability against settling.

Common examples of colloids include milk (emulsion), fog (aerosol), butter (gel), and paint (sol). These examples highlight how colloids are part of everyday life.

Thus, the correct answer is that the size of colloidal particles lies between true solutions and suspensions. This makes option C (In between true solution and suspension) the correct choice.