Final answer:
The coelomic cavity in a clam can be located in the visceral mass, which is situated above the foot and contains several vital organ systems.
Step-by-step explanation:
When dissecting a mollusk such as a clam, you would locate the coelomic cavity in the visceral mass. The visceral mass is a region above the foot in the mollusk's anatomy that contains several organ systems, such as the digestive, nervous, excretory, reproductive, and respiratory systems. While mollusks are schizocoelous eucoelomates, the coelomic cavity in adult mollusks has been mostly reduced and is now primarily limited to the region around the heart. However, remnants of the coelomic cavity can sometimes be found surrounding the gonads, portions of the kidneys, and the intestine. Therefore, the correct answer is (c) In the visceral mass.