Question

Tyndall effect is observed when sunlight passes through canopy of a dense forest because:
A) In the forest, mist contains tiny droplets of water which act as particles of colloid dispersed in air.
B) In the forest smog, fog is present which contains droplets of water which act as particles of colloid dispersed in air.
C) In the forest, tree leaves contain chloroplast which contains guard cells, which act as particles of colloid dispersed in air.
D) All of the above.

Answer 1

We know that Tyndall effect is shown by colloids which are heterogeneous mixtures made of dispersed phase and dispersing medium.

Complete answer:
We all are surrounded by mixtures which can be categorized as homogeneous mixtures and heterogeneous mixtures based on the uniformity of the composition. We can categorize those mixtures which have uniform composition throughout as homogeneous ones with examples of sugar solution. On the other hand, the mixtures in which composition is non-uniform can be categorized as heterogeneous mixtures.
We have further classification of heterogeneous mixtures as suspensions and colloids depending upon the size of the particles. The particles in the suspensions are large enough that we can see them with our naked eyes but that is not possible in colloids yet light can be scattered by the particles in both cases.
In colloids we have two components namely dispersed phase and dispersing medium. The particles constitute the dispersed phase whereas the medium in which they are suspended is called the dispersing medium. For example, in foam, the dispersed phase is gas and the dispersing medium is solid.
Tyndall studied and explained the phenomenon of scattering of light by colloid particles even when they are invisible to the naked eye and this effect is called the Tyndall effect.
We can observe the Tyndall effect around us in many situations. For example, in movie halls, the dust and smoke particles can scatter the light; or in misty mornings.
Here, we will talk about the Tyndall effect observed in forest. The dust particles present in the air become the surface for condensation of moisture and fine droplets are formed which are colloidal in nature. They keep floating in air as mist and can scatter the light resulting in Tyndall effect.

Hence, the correct option is A.

Note: We have to be careful with smog and fog as both are colloids but smog is seen in polluted environments not in forests. Similarly, guard cells are not suspended anywhere as particles but are present in all the green leaves in our out of the forest.