Hello Sachin ,

The solution of oleic acid spreads very fast on the surface of water . It forms thin layer with some thickness of only one molecule . Why because oleic acid has low density compared to water so , this is the reason why oleic acid float on water .

It belongs to category called lipids generally these are commonly called as "Fat Molecule"  it have both hydrophilic (Molecules which are dissolves in the water ) and hydrophobic (Molecules which are not soluble in water) parts .

I think this answer will helps you lot .

All the best !!!!