Final answer:
Most perfumes would be less dense than water due to their composition, typically consisting of oils and alcohols, and hence would float on top of the water.
Step-by-step explanation:
To determine whether perfume would be more or less dense than water, we can refer to the principle that a substance's relative density compared to water dictates whether it will float or sink. Since water has a density of 1.0 g/mL, a substance with a density less than this will float on water, and a substance with a density greater than this will sink. Perfumes typically contain a mixture of various oils and alcohols, which have densities less than water, so most perfumes would be less dense than water and would float on top. This is similar to how oil, which is less dense than water, floats on the surface.
As an example, if a block of polystyrene has 90% of its volume floating above the water's surface, this indicates that the polystyrene's density is less than the water. Given that the density of water is 1000 kg/m³, the polystyrene's density would be such that only enough of it submerges to displace a weight of water equal to its own weight, resulting in most of the volume remaining above water.