Final answer:
The qualities of a square that are proportional to its diagonal length include the area and the square of the diagonal itself, both of which grow proportionally to the square of the side length of the square.
Step-by-step explanation:
The question pertains to the properties of a square proportional to its diagonal length.
In a square, the area and the square of the diagonal have a direct proportionality.
If you denote the side length of a square as L, then the diagonal (d) can be expressed using the Pythagorean theorem as d = L√2.
Thus, the square of the diagonal is L²×2, which means it grows proportional to the square of the length (length²).