Try it on paper first. A hint, the key idea and the worked solution are here when you need them.
Solution: particles under , invisible, never settle, pass through filters, do not scatter light. Colloid: to , never settle, cannot be filtered, scatter light (the Tyndall effect). Suspension: large particles that can be seen, settle and can be filtered.
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) Fog is a colloid: tiny drops of water spread through air. The drops scatter the light sideways into our eyes, so the path of the beam is seen. This is the Tyndall effect. Clear air has almost nothing to scatter the light.
Step 2. (b) Yes. Smoke is a colloid of tiny solid particles in air, and they scatter light too.
Answer: The fog's tiny drops scatter the light (the Tyndall effect); smoke does the same.
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