The body cavity of Ascaris is pseudocoel as

The correct option is "bound extremely by muscle layer and internally by intestines".

A true body cavity (coelom) is a fluid-filled cavity between the body wall and the gut wall that is completely lined by mesoderm on both sides (i.e., both the outer boundary and the inner boundary are lined by mesodermal epithelium).

In the case of Ascaris (which belongs to the phylum Aschelminthes/Nematoda), the body cavity is classified as a pseudocoel (false coelom) because it is not completely lined by mesoderm. Instead, the mesoderm is present only as an outer muscular layer lining the body wall (ectoderm-derived), while the inner side of the cavity is lined directly by the gut/intestine wall (which is endoderm-derived) without a mesodermal lining.
Thus, the pseudocoel is bound externally by the muscle layer (mesodermal) and internally by the intestines (endodermal).