Which of the following statements is true?
(a) phospholipids will spontaneously form liposomes in nonpolar solvents.
(b) in eukaryotes, all membrane-enclosed organelles are surrounded by one lipid
bilayer.
(c) membrane lipids diffuse within the plane of the membrane.
(d) membrane lipids frequently flip-flop between one monolayer and the other.

The correct answer is: C) Membrane lipids diffuse within the plane of the membrane.

Explanation:

Membranes are mostly made from phospholipids that, in aqueous environments, are arranged forming two layers (the hydrophilic heads are in contact to both the intercellular and extracellular spaces, and the hydrophobic tails make contact to one another in amidst the layers). These lipids that make up the bilayer diffuse laterally within the plane of the membrane and thus constitute the fluid mosaic model of cell membranes.

the correct option is option d