Final answer:
Unity is the principle that provides a feeling that a design is a single unit and occurs when all the principles and elements blend together in a visually harmonious way.
Step-by-step explanation:
The principle that provides a feeling that a design is a single unit and occurs when all the principles and elements blend together is unity.
Unity in a design creates a sense of completeness, cohesiveness, and visual harmony. It is the opposite of chaos or fragmentation. When all the elements and principles work together in a design, they create a sense of unity.