Colloid science fundamentals:\nWhat is the typical size range of colloidal particles (expressed in millimicrons or nanometers)?

Introduction / Context:
Colloids are dispersions where the dispersed-phase particles are intermediate in size between true solutions and suspensions. Recognizing their size scale is crucial for predicting optical behavior (Tyndall effect), stability, and separation methods.

Given Data / Assumptions:

• Classical colloid size range is typically cited as about 1 nm to 1000 nm (10 to 10,000 Å). Many textbooks emphasize a practical working range within these limits.
• Units: 1 millimicron = 1 nm; 1 Å = 0.1 nm.

Concept / Approach:
True solutions contain molecular or ionic species < 1 nm. Suspensions have particles generally > 1 μm (1000 nm). Colloids occupy the middle ground. In many practical contexts, 5–200 nm is often quoted as a representative colloidal size window for stability and optical effects in common systems.

Step-by-Step Solution:

Verification / Alternative check:
Textbook ranges vary slightly, but the essence remains: colloids are between solution-sized species and coarse suspensions, with tens to hundreds of nanometers being archetypal.

Why Other Options Are Wrong:

• (b), (c), (e): Particle sizes are too large; these are suspensions.
• (d): Too small and close to true solution sizes for most colloidal behaviors.

Common Pitfalls:
Confusing the borderline between large molecules and small colloids, or equating visibility under optical microscopes with colloidal classification. Always check the nanometer scale.

Final Answer:
5 – 200 millimicrons (≈ 5 – 200 nm)