Which of the following is true for the diagonals of a rhombus?

In a rhombus, one of the defining characteristics is that the diagonals are always perpendicular to each other. This means that when they intersect, they form right angles (90 degrees). This property is a result of the symmetry inherent in rhombuses, where each side is of equal length and the diagonals bisect each other. Additionally, while the diagonals do indeed bisect each other and contribute to the overall symmetry of the shape, it’s their perpendicular intersection that is a quintessential property that distinguishes rhombuses from other quadrilaterals.

The statement about being unequal in length does not hold true for rhombuses, as one diagonal can be longer than the other, but this fact alone does not define a rhombus. The diagonals do bisect each other, which is contrary to the description provided in one of the other options. Lastly, although the sides of a rhombus are parallel to each other, the diagonals themselves are not parallel to the sides; they intersect at the center of the shape.

Thus, the property of the diagonals being perpendicular is a fundamental characteristic of rhombuses, making this option the correct choice.