Question

(a) What is the diameter, in micrometers, of a spherical ink
droplet from an early version of an ink-jet printer if the volume of
the droplet is 200 ± 10 pL?

If the ink has a density of
1.1 g/mL, what is the mass in
milligrams of ink in a droplet
from this printer? Is
“milligrams” an appropriate
unit for describing this mass?

Answer 1

I would convert volume of 200 pL to mL then calculate the diameter of the sphere. Go from there to mass.

Answer 2

That's probably not the easiest way to do it. Remember that 1 cubic decimeter is 1 liter; therefore, convert the volume in pL to liters then to cubic decimeters, the determine the diameter. The answer will be in decimeters which you can convert to micrometers.
For the mass, the mL conversion probably is the way to go.