Question

Select all that apply to colloids.
A.) A colloid is a mixture intermediate between heterogeneous and homogenous. B.) Colloids cannot be separated by filtration.
C.) Colloids can be seen using an optical microscope.
D.) Fog and smoke are examples of colloids.
E.) The Tyndall effect is a test to determine whether or not a mixture is a colloid.

Answer 1

The following applied to colloids:
1. They can not be separated by filtration. This is because colloids are uniform and homogeneous in nature. They do not produce sediments when left standing.
2. Colloids can be be seen using optical microscope. This is because, the diameter of the dispersed particles range from 1 to 1000 nanometer. This size range can easily be seen under optical microscope.
3. Fog and smoke are example of colloids. Smoke is a type of colloid in which solid is dispersed in gas while in fog, liquid is dispersed in gas. 
4. The Tyndall effect is a test that determine whether or not a mixture is a colloid. Light is dispersed by colloidal particles. 

Answer 2

Answer: All the points apply for colloids.

Explanation: This question can be answered only by looking at the properties of colloids:

1. The particle size of these systems range from 1nm to 1mm.
2. These are generally considered as heterogeneous mixtures but have some properties of homogeneous mixtures. There is some physical boundary present between solute and solvent.
3. These solutions cannot be separated by ordinary filtration.
4. Tyndall effect: This effect is generally seen in colloidal solutions or solutions having very fine suspension. This effect is basically the scattering of light by the particles. This effect can be seen in the sky when sunlight is scattered by clouds.
5. These solutions have small particle size thus it cannot be seen from bare eyes, thus we need optical microscope.
6. Cloud, Milk, Fog and Smoke are some of the examples of Colloidal solutions.

These properties enlisted above show that all the points given in the question are correct for colloidal solutions.