The right option for the statement “Tyndall effect is exhibited by”, is :

The correct option is Starch solution.

To understand why a starch solution exhibits the Tyndall effect, let us break down the underlying concepts step-by-step:

1. What is the Tyndall effect?
The Tyndall effect is the phenomenon where a beam of light is scattered by particles in a colloid or a very fine suspension. When light passes through such a mixture, the particles scatter the light waves, making the path of the light beam visible to an observer.

2. Particle Size and Scattering:
For scattering of visible light to occur, the size of the dispersed particles must be comparable to the wavelength of light.
In true solutions (like NaCl, glucose, and urea solutions), the solute particles exist as individual ions or small molecules. Their diameters are less than:
$1\text{nm}$
Because these particles are so small, they do not scatter light, and the path of the light beam remains invisible.
In colloidal solutions (like a starch solution), the particles are macromolecules or aggregates whose sizes lie in the colloidal range:
$1\text{nm}$ to $1000\text{nm}$
These particles are large enough to scatter visible light.

3. Classification of the Options:
- NaCl solution: Forms a true solution where sodium and chloride ions dissolve completely. It does not exhibit the Tyndall effect.
- Glucose solution: Forms a true molecular solution. It does not exhibit the Tyndall effect.
- Urea solution: Forms a true molecular solution. It does not exhibit the Tyndall effect.
- Starch solution: Forms a lyophilic colloidal system (sol) in water. The starch molecules are large enough to be in the colloidal range, making it scatter light and show a clear Tyndall effect.