Final answer:
The c) hydroxyl (OH) group in prostaglandin analogs enables them to bind to the FP receptor, specifically noted in the PGF subtype where -OH groups are present at critical positions.
Step-by-step explanation:
The functional group that allows a prostaglandin analog to bind to the FP receptor is the c) hydroxyl (OH) group. Prostaglandins are derivatives of fatty acids such as arachidonic acid and contain various functional groups that define their classification and function.
Specifically, the PGF subtype of prostaglandins, which would bind to the FP receptor, contains -OH groups at all the three positions.
The nomenclature of prostaglandins emphasizes the substituent patterns where F indicates the presence of 1,3-diol groups in the ring structure. Therefore, the correct answer to the question is the hydroxyl (OH) group.