Which of the following is the homogeneous solution of resins in the alcohol?
Solution vs. Suspension in Coatings
This question hinges on the difference between a solution and a suspension. A homogeneous solution is a mixture where the components are uniformly mixed and cannot be visually distinguished (e.g., salt dissolved in water). A suspension is a mixture where solid particles are dispersed, but not dissolved, in a liquid (e.g., sand in water). Paints are suspensions, while varnishes are true solutions.
📝 Detailed Analysis of the Options
(a) Distemper
Composition: Distemper is a water-based paint. It is a suspension of solid particles like chalk and pigments in water, with glue as a binder.
Analysis: It is not a solution, it is not made with resin, and its solvent is water, not alcohol. Therefore, it is incorrect.
(b) Enamel paint
Composition: Enamel paint is a suspension of solid pigments in a varnish vehicle.
Analysis: Although its liquid vehicle (varnish) is a solution, the final paint product is an opaque suspension because of the added pigments. It does not fit the description of a homogeneous solution.
(c) Plastic paint
Composition: Plastic paint (emulsion) is a water-based suspension (or more accurately, an emulsion) of plastic polymer particles and pigments.
Analysis: Like distemper, it is a suspension, and its liquid base is water, not alcohol. Therefore, it is incorrect.
(d) Varnish
Composition: This is the correct answer. Varnish is, by definition, a homogeneous solution created by dissolving a resin (like shellac, gum, or copal) in a solvent.
Analysis: When the solvent used is alcohol or spirit, the resulting product is specifically called a **spirit varnish**. French polish is the most famous example of a spirit varnish, made by dissolving shellac resin in alcohol. This perfectly matches the description in the question.
📊 Comparison of Coatings
| Coating Type | Mixture Type | Key Components | Solvent |
|---|---|---|---|
| Varnish (Spirit) | Homogeneous Solution | Resin (Shellac) + Alcohol | Alcohol |
| Distemper | Suspension | Chalk + Pigment + Glue + Water | Water |
| Enamel Paint | Suspension | Pigment + Varnish | Oil/Turpentine |
| Plastic Paint | Suspension / Emulsion | Polymer + Pigment + Water | Water |
