Solution

A phospholipid is a lipid-containing phosphate group and the main constituent of cell membranes. It consists of a hydrophobic(water-fearing)tail and hydrophilic(water-loving) head. It is a triglyceride in which fatty acid is replaced by a phosphate group. This layer follows the rule of 'like dissolves like', the hydrophilic head dissolves readily in water. Similarly, the hydrophobic tail is dissolved in non- polar molecules. This property of phospholipid limits the permeability of the membrane.
So, the correct answer is " phospholipids ".