The SI unit of mass is kilogram. 1 gram is 1/1000 of a kilogram. The unit for volume is derived from the unit of length which is meter as m^3. Another commonly used unit of volume is liter. The relation between the two is 1 m^3 = 1000 L.
To determine the density of the liquid in the bottle divide the mass by the volume. The mass of the liquid is 100 g and the volume is 200 mL. In terms of g/mL the density of the liquid is 1/2 = 0.5 g/mL. If the density has to be expressed in SI units it requires the conversion of grams to kilograms and mL to m^3. This gives the density of the liquid as (0.1)/(0.0002) = 500 kg/m^3.