We know that: `"Density of substance =("Mass of substance ")/("Volume of substance ")`
Here Mass of substance = 50 g
And Volume of substance `=20 cm^(2)`
So Density of substance `=(50 g )/(20 cm ^(3))`
`=2.5 g cm^(-3)`
Since the density of substance `(2.5 g cm ^(-3)` is greater than the density of water `(1 g cm^(-3))`, therefore , the substance will sink in water .