Answer: D) a pure substance and an element
Step-by-step explanation:
Mercury is an element which is composed of similar atoms and is a pure substance.
Element is a pure substance which is composed of atoms of similar elements.
Compound is a pure substance which is made from atoms of different elements combined together in a fixed ratio by mass.
Mixtures are impure substances and are heterogeneous materials as they do not have uniform composition and the components are not evenly distributed throughout the material.