Here's why:

* Orthorhombic Structure: The iodine molecules (I₂) arrange themselves in a repeating pattern where the unit cell has three unequal axes at right angles to each other. This results in a rectangular prism shape.

* Cubic Structure: A cubic structure would have three equal axes at right angles, forming a cube.

Therefore, solid iodine's structure is not cubic but rather orthorhombic.