Tyndall Effect

Concept: The Tyndall effect is the scattering of a beam of light as it passes through a colloid or a very fine suspension. The individual suspension particles or colloidal particles scatter and reflect light, making the beam visible from the side. Step 1: Understanding the Tyndall Effect For the Tyndall effect to be observed:
The diameter of the dispersed particles must be roughly in the range of the wavelength of light (approximately 40 nm to 900 nm).
There must be a significant difference in the refractive indices of the dispersed phase and the dispersion medium. True solutions (where solute particles are individual ions or small molecules, typically<1 nm) do not show the Tyndall effect because the solute particles are too small to scatter visible light effectively. Step 2: Classifying the given options
(1) Salt solution (e.g., NaCl in water): This is a true solution. Salt dissolves to form individual ions (Na and Cl ) which are too small to scatter light. It will not show the Tyndall effect.
(2) Sugar solution (e.g., sucrose in water): This is also a true solution. Sugar dissolves as individual molecules which are too small to scatter light. It will not show the Tyndall effect.
(3) Milk: Milk is a colloid, specifically an emulsion of fat globules dispersed in an aqueous solution. It also contains casein protein micelles. The fat globules and protein micelles are large enough (colloidal size range) to scatter light. Therefore, milk shows the Tyndall effect (e.g., a beam of light passing through milk will be visible).
(4) Copper sulphate solution ( in water): This is a true solution. Copper sulphate dissolves to form Cu and SO ions, which are too small to scatter light. It will not show the Tyndall effect (it appears clear, though colored blue). Step 3: Identifying which shows the Tyndall effect Based on the classification, Milk is a colloid and will exhibit the Tyndall effect. Salt solution, sugar solution, and copper sulphate solution are true solutions and will not.

Step 1: Understand the Tyndall effect.
The Tyndall effect is the phenomenon where light is scattered by particles in a colloid or a fine suspension, making the path of the light visible. This effect is observed when the dispersed particles are large enough to scatter light, but small enough that they do not settle out of the dispersion. True solutions (like distilled water, sugar solution, and ethanol) have particles that are too small to scatter light effectively, so they do not show the Tyndall effect. Step 2: Classify the given options based on particle size.
Distilled water: A pure substance, essentially a true solution, with particles too small to scatter light.
Sugar solution: A true solution where sugar molecules are dissolved in water; their size is too small to cause significant scattering.
Ethanol: A pure substance, or if considered in solution with water, forms a true solution. Particles are too small.
Starch solution: Starch in water forms a colloidal dispersion (or a fine suspension, depending on concentration and preparation). The starch particles are large enough to scatter light. Step 3: Determine which solution will exhibit the Tyndall effect. Based on the principle that only colloids and fine suspensions exhibit the Tyndall effect, starch solution is the correct answer because it forms a colloidal dispersion. $ $