The mass law is LAW OF CONSERVATION OF MASS.
The law of conservation of mass states that mass, in an isolated system is neither created nor destroy by chemical reaction or physical transformations.
This implies that, the mass of the chemicals before the reaction will be equal to the mass of the product after the reaction.
Density = mass/volume
substituting the given values :
We get :
D = 37.4 / 2.2 x 10^3
D = 0.017 grams/liter
The definition of a transition metal is that it must have an incompleted sub-level in one or more of its oxidation states. As zinc has a completed sub-level at all oxidative states, so it can't be considered a transition metal.