Tyndall effect can be used to distinguish between:

The correct answer is Option (3) → Sugar solution and starch solution

The Tyndall effect is the scattering of light by colloidal particles, which makes the path of a light beam visible. It is seen only when the dispersed particles are not much smaller than the wavelength of light. A sugar solution is a true solution (molecular size particles) and shows no Tyndall cone, while starch forms a colloidal solution (macromolecules) and scatters light. So the Tyndall effect distinguishes these two.

Why the other options are incorrect

• Option (1) Lemonade and sand solution — Incorrect. Sand does not form a solution or a colloid; it settles as a suspension and is told apart by sight, not by the Tyndall effect.

• Option (2) Sugar solution and salt solution — Incorrect. Both are true solutions; neither shows the Tyndall effect.

• Option (4) Lemonade and sugar solution — Incorrect. Lemonade (sugar, salt and lemon juice in water) is essentially a true solution, like sugar solution, so the two cannot be told apart this way.

Note: This question is from the pre-rationalised NCERT book (2022-23). The topic is not there in the latest NCERT book (2026-27), and it is also out of the CUET 2026 syllabus.

NCERT (Pre-rationalised edition, 2022-23):
Tyndall Effect – “If a homogeneous solution placed in dark is observed in the direction of light, it appears clear and, if it is observed from a direction at right angles to the direction of light beam, it appears perfectly dark. Colloidal solutions viewed in the same way may also appear reasonably clear or translucent by the transmitted light but they show a mild to strong opalescence, when viewed at right angles to the passage of light, i.e., the path of the beam is illuminated by a bluish light.”