Density of fresh egg = 1.2 g/cm³.
Density of spoiled egg = Density of fresh egg - 0.3 g/cm³.
Density of spoiled egg =( 1.2 - 0.3 ) g/cm³ = 0.9 g/cm³.
Now, it is given that any object with density less than 1 g/cm³ will float on water.
To tell whether an egg is spoiled or not using water. We should drop egg in water if it float then it is spoiled else it is fresh.
Hence, this is the required solution.