Question

what is the mass of 1. a drop of water
                              2. a drop of oil
                              3. a drop of ethanol

Answer 1

Density is the ratio of mass to volume for a material.ρ = mV
so the mass will depend upon the density of the material and the volume. if you take the volume to be same that is one drop of same size than just calculate the mass by putting the value of density of each material. water is 1000 kg/m3. just take the drop radius to be 1 cm and calculate the volume, then put the value of density. you have not mentioned what oil. as different oils will have different density.