Answer is Gasoline.
Explanation: For determining which substance will float, it can be determined with the values of density.
Density of Milk = [tex]1.026gm/cm^3[/tex]
Density of Gasoline = [tex]0.702gm/cm^3[/tex]
The one with lower density will float and the one with more will sink.
So here, we can see that the density of gasoline is less therefore, this will float.