The Tyndall effect is not observed in:

Particles scattering a light ray in a colloid or in a very tiny suspension is all that the Tyndall effect is. Another name for it is Tyndall dispersion.
Longer wavelengths transmit more light under the Tyndall effect, but shorter wavelengths are easily dispersed through scattering. When the light-scattering particulate matter is additionally spread in an otherwise light-transmitting medium, the Tyndall effect is seen or noticed. The particles' diameter should be in the range of 40 to 900 nm, or fairly close to the visible light spectrum (400-740 nm). The Tyndall effect is primarily applicable to suspensions and colloidal mixes with particle sizes that are close to the ideal particle range. However, the Tyndall effect is not seen in a real solution because the particles' small width prevents them from scattering much light.

Colloidal solutions are those in which the size of particles is not visible to naked eyes but they can scatter the beam of light.

A true solution is a homogeneous mixture of two or more components. One of the properties of a true solution is that their particle size should be smaller than 1 nm and they should not be visible to the naked eye.

The true solution does not show the Tyndall effect.

Hence, the correct option is D.