Which phylum to not have an internal or external skeleton or shell?

exoskeleton (from Greek έξω, éxō "outer" and σκελετός, skeletós "skeleton"[1]) is the external skeleton that supports and protects an animal's body, in contrast to the internal skeleton (endoskeleton) of, for example, a human. In usage, some of the larger kinds of exoskeletons are known as "shells". Examples of animals with exoskeletons include insects such as grasshoppers and cockroaches, and crustaceans such as crabs and lobsters, as well as the shells of certain sponges and the various groups of shelled molluscs, including those of snails, clams, tusk shells, chitons and nautilus. Some animals, such as the tortoise and turtle (shell page), have both an endoskeleton and an exoskeleton.

Phylum Cnidaria

Explanation:

They do not have internal or external skeleton.

ability to bond woth oxygen

the answer is c) an oak tree