Which characteristic of a phospholipid contributes to the fluidity of the membrane?
its head
cholesterol
a saturated fatty acid tail
double bonds in the fatty acid tail

Double bonds in the fatty acid tail is the characteristic of a phospholipid contributes to the fluidity of the membrane .

Explanation:

Phospholipid -

The phospholipid has a hydrophobic region or the water hating , and is a non - polar region , hence , it can interact with the non - polar molecules in a chemical reaction .

And phospholipid has a hydrophilic region or the water loving , and is a polar region , hence , this region can form hydrogen bond with water .

Hence ,

When , a phospholipid is placed in water , it forms a ball or a cluster .

The two hydrophobic tails and the hydrophilic head together forms a phospholipid molecule .  

The hydrophilic region have a  phosphate-containing group which is attached to the glycerol molecule and the hydrophobic tails have unsaturated fatty acid and are the long chain hydrocarbon .