How does unity create mood, or emotion, in the artwork?

In art, what does the term, “form” mean? a. the pleasing arrangement of parts or objects, along with the characteristics shared between the objects. b. any three dimensional geometric shape. it can also refer to the visible elements of a piece. c. the sense of balance achieved by placing objects or forms that are different on either side of a central line. d. the relationship, either of time or space between recurring elements of a composition.