Final answer:
A suture is the weakest fibrous joint and is functionally classified as a synarthrosis, which is an immobile joint.
Step-by-step explanation:
Structurally, a suture is considered the weakest among the fibrous joints due to the narrow gap filled with fibrous connective tissue that unites the skull bones, providing protection for the brain. Functionally, it is classified as a synarthrosis, which means it is an immobile joint.
Thus, the correct answer to the question is:
- Suture - Synarthrosis