Final answer:
The most common number of carbons in fatty acid hydrocarbon chains of membranes is 18.
Step-by-step explanation:
The most common number of carbons in fatty acid hydrocarbon chains of membranes is 18. Fatty acids are building blocks in lipids and can have chain lengths ranging from 4 to 36 carbons. However, the most common fatty acids in membranes typically contain 12–18 carbons. For example, palmitic acid is a saturated fatty acid with 16 carbons, while stearic acid is also a saturated fatty acid with 18 carbons. These fatty acids contribute to the structure and function of cell membranes.