A nucleus which lacks a nuclear membrane as found in the members of Kingdom Monera is called as a

The correct option is A nucleoid
The nucleoid is a primitive nucleus which contains the single DNA which is coiled around itself. This genetic material is not enclosed by the nuclear membrane. This is a characteristic feature of the prokaryotes.

Karyon is the synonym of nucleus.
A true nucleus has a nuclear membrane surrounding the nucleoplasm in which we find the DNA condensed into chromosomes and the presence of a nucleolus.