The volume of the block is (2cm x 4cm x 2cm) = 16 cm³ .
Density = (mass) / (volume)
= (20 gm / 16 cm³) = 1.25 gm/cm³ .
The block will float in any liquid whose density is 1.25 gm/cm³ or more,
such as bromine (3.12), carbon disulfide (1.26), carbon tetrachloride (1.58),
chloroform (1.47), freon refrigerant (1.48), glycerine (1.26), mercury (13.6),
nitric acid (1.56), sulfuric acid (1.84).
It will sink in any liquid whose density is less than 1.25 gm/cm³, such as
acetic acid (vinegar) (1.05), rubbing alcohol (0.8), beer (1.01), butane (0.6),
castor oil (0.96), Texas crude oil (0.87), unleaded gasoline (0.74), milk (1.03),
olive oil (0.86), brine (1.23), liquid oxygen (1.14), pure water (1.000).