SPECIFIC QUESTION TO ANSWER:

A$.$ How long will it take a $100nm$ Corona Virus to settle is the ground from a height of $1m?$

To do this you will need to derive a general expression based on Newton law: $ma=F$

i$.$e$.$ you have a gravity force and a drag force. For drag force use Stokes law: $F_{\text{d}\text{r}\text{a}\text{g}}=3DV$

where: $$ is viscosity of air; $D=$ particle diameter; $V$ is settling velocity.

In order to solve Newtons equation assume that the system has reached steady state, so that there is no acceleration.

What can you conclude about coronavirus gravitationally settling in a room, based on your calculation?

B$.$ Do the same calculation for a $10$ micron droplet that would contain virus.