Answer: 
The cube of gold will have the greatest mass. 
Explanation: 
All the cubes have the same size, so they have the same volume. 
The property that varies among the cubes is density. 
D = m/V Multiply both sides by V and transpose. 
m = DV 
Since V is a constant, m ∝ D. 
That is, the cube with the greatest density will have the greatest mass. 
The observed densities are 
Iron = 7.9 g/cm³ 
Brass = 8.5 g/cm³ 
Lead = 11.4 g/cm³ 
Gold = 19.3 g/cm³ 
Gold has the greatest density, so the cube of gold has the greatest mass.