Question

A true solution does not show Tyndall effect, because of the:

• A. Nature of solvent
• B. Amount of solute
• C. Size of the particles
• D. Nature of solute

Hint:

The Tyndall effect is observed when light is scattered by larger particles (colloidal particles) in a medium, not by small particles in a true solution.

Answer 1

The Correct Option is C

Understanding the Concept:
The Tyndall effect is the scattering of light by particles suspended in a medium, the same reason a beam from a car's headlight becomes visible in foggy air.

Key Formula or Approach:
Light scattering by a particle becomes noticeable only when the particle's size is comparable to or larger than the wavelength of visible light, roughly 400 to 700 nanometres, or at least in the range colloids occupy (about 1 to 1000 nanometres).

Detailed Explanation:
In a true solution, the solute exists as individual ions or molecules, typically under 1 nanometre across, hundreds of times smaller than the wavelength of light. Compare this with a colloid, such as milk or starch solution, where particles are much bigger, large enough to deflect light and make the beam visible. A true solution simply does not have particles in that size range, so the light travels through it without being scattered.

Final Answer:
A true solution fails to show the Tyndall effect because its particles are too small in size to scatter light.

Answer 2

We can also reason this out by asking what physical property actually governs light scattering, independent of chemistry.

1. Nature of solvent: Whether the solvent is water or an organic liquid affects things like boiling point and polarity, but it has no direct bearing on whether the solute particles inside it are big enough to scatter light.
2. Amount of solute: A more concentrated true solution still has particles at the molecular or ionic level; concentration changes how much solute is present, not the size of each individual particle.
3. Size of the particles: Light scattering is a size-dependent phenomenon; particles need to be at least in the low nanometre-to-micrometre range to bend light noticeably, and true-solution particles fall well below that.
4. Nature of solute: Two different solutes, say table salt and glucose, both form true solutions with equally invisible light paths, showing that it is not what the solute chemically is that matters, but how small its particles end up.

Physically, only particle size controls whether light gets scattered, and true-solution particles are simply too small for that to happen.

So the correct answer is size of the particles.