Which of the following nanomaterials has one dimension less than $100 \ nm$?

The precipitation power of an electrolyte increases with:

Fog is a colloidal solution of

According to the Hardy-Schulze rule,the flocculating power of an ion increases with:

Identify the correct statements from the following :
$I$. Sulphur sol is an example of a multimolecular colloid.
$II$. Tyndall effect is observed when the diameter of the dispersed particles is not much smaller than the wavelength of the light used.
$III$. The process of removing a dissolved substance from a colloidal solution by means of diffusion through a suitable membrane is called peptisation.
$IV$. Eosin,gelatin are examples of negatively charged sols.

How does it become possible to cause artificial rain by spraying $AgI$ on the clouds?