ANSWER
![E.8\sqrt[]{2}](https://img.qammunity.org/2023/formulas/mathematics/college/9qw5slxnku1esrtn9zicgjxn5q3tdio8p5.png)
Step-by-step explanation
The square has a perimeter of 32.
The perimeter of a square is given as:

where L = length of the side of the square
Therefore, we have that for the given square:

The square has sides 8 units long.
To find the length of the diagonal, apply Pythagoras theorem, since the diagonal forms a right triangle with the sides of the square:

where hyp = hypotenuse of the triangle (diagonal)
a, b = legs of the triangle (side lengths of the square)
Therefore, we have that:
![\begin{gathered} D^2=8^2+8^2 \\ D^2=64+64=128 \\ D=\sqrt[]{128} \\ D=8\sqrt[]{2} \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/yl0xd7xpyhuurqyvmm8b6vgnprqx9dx5ef.png)
That is the length of the diagonal.