The best description of the Tyndall effect in a colloid is: The Tyndall effect is the scattering of light as it passes through a colloidal mixture. In a colloid, the dispersed particles are large enough (typically in the range of about 1 to 1000 nanometers) to scatter light, making the path of the light beam visible. This scattering occurs because the colloidal particles are similar in size to the wavelength of visible light, causing light to scatter in all directions. As a result, when a light beam is shined through a colloid, the beam becomes visible due to this scattered light, unlike in a true solution where the particles are too small to scatter light and the beam passes through without being seen. The Tyndall effect is used to distinguish colloids from true solutions and has practical applications such as determining particle size and density in aerosols and colloidal suspensions

. In summary:

• The Tyndall effect is light scattering by colloidal particles.
• It makes the light beam visible as it passes through the colloid.
• It does not occur in true solutions because their particles are too small.
• It is a key method to identify colloidal mixtures.

This explanation captures the essence of the Tyndall effect in colloids accurately and concisely.