Question

The particle size in a colloidal solution is:

• A. 1 Å – 10 Å
• B. 10 Å – 2000 Å
• C. More than 2000 Å
• D. Less than 1 Å

Hint:

Colloidal solutions have particle sizes in the range of 10 Å to 2000 Å, which is why they exhibit the Tyndall effect.

Answer 1

The Correct Option is B

Picture three familiar mixtures side by side: salt water, milk, and muddy water. Milk is the working example of a colloid here.

1. 1 Å - 10 Å: particles this size behave like the dissolved salt in salt water. They never scatter light and never settle, which is a true solution's range, not milk's.
2. 10 Å - 2000 Å: particles this size behave like the fat and protein in milk, staying evenly spread through the water without settling while still scattering a light beam. This matches milk's known particle size.
3. More than 2000 Å: particles this size behave like the mud in muddy water, heavy enough to sink, which is not how milk behaves.
4. Less than 1 Å: this is smaller than any real dispersed particle and does not match milk or any of the other mixtures.

Since milk's particles fall in the same size band that gives colloids their light-scattering, non-settling behavior, the correct answer is 10 Å - 2000 Å.

Answer 2

Line up the three types of mixtures by particle size, from smallest to largest: true solution, then colloid, then suspension. Check each option against that scale.

1. 1 Å - 10 Å: this is the smallest band on the scale, where particles are single ions or molecules. That band belongs to a true solution, not a colloid.
2. 10 Å - 2000 Å: this sits in the middle of the scale, above the true-solution band and below the suspension band. A colloid occupies exactly this middle zone.
3. More than 2000 Å: this is the largest band on the scale, reserved for suspensions, where particles are big enough to be seen and to settle.
4. Less than 1 Å: this falls below even the true-solution band and does not correspond to any real dispersed particle size.

The middle band, 10 Å - 2000 Å, is where colloidal particles sit on the scale, so that is the correct answer.