about fog and grammar

Fog is droplets of water vapour suspended in the air. Does that make fog a collective noun? A collective noun is a noun that is singular in form but refers to a group of people or things. A group is any number of entities considered as a unit. Whilst these definitions tell me that fog is a collective noun neither of these tell me how many droplets you need before you properly have fog. Cloud is also droplets of water vapour suspended in the air. Is cloud a collective noun? Probably. Is cloud fog?

You can try to take pictures of fog. You may fail. Here you can see that I have failed. Droplets of water vapour have obscured my lens. I do not know if they were cloud, fog or ungrouped non-collective discrete droplets.