The diagrams in Figure 1 show the sub-microscopic arrangements of particles in five different boxes, labelled A, B, C, D, and E. Each circle represents an atom; white circles represent atoms of one element, and solid black circles represent atoms of another element.

Using Figure 1, identify:
Which box represents a single, pure compound?
Which box represents a mixture of elements?
Which box represents a mixture of an element and a compound?