Finally my question has been answered after sometime; thx to my dear lecturer!
1 mL is a measure of volume, while 1 g is a measure of mass.
The property that relates these two is density, where;
density = mass/volume
for water, the density at room temp and pressure is 1 g/mL.
Thus, ONLY for water, we can assume that 1 mL of water will
have a mass of 1 g.
for mercury, the density is 13.5 g/mL. Therefore, 1 mL of
mercury would weigh at 13.5 g, NOT 1 g.
