Which molecule is less soluble in water--a fat or a phospholipid? Why?

Fat is less soluble in water compared to phospholipids.

This is because, fat is made up of three molecules of fatty acids which are not polar in nature at all, thus they mixed very poorly with water.

Phospholipids on the other hand has its molecules divided into two distinct regions, the head and the tail region. The head region is hydrophillic and it is polar in nature, that is, it mixes well with water. The tail region is made up of the fatty components and it is hydrophobic.

Because of this difference in structure, phospholipid will dissolve better in water.

A fat molecule is less soluble in water because it has three non-polar fatty acids and no polar or charged head like a phospholipid has.