This undoubtedly has to be a rhombus. When you look at other quadrilaterals for example and want to judge and or differentiate, we see that in the case of a square, the diagonals are equal to one another and they are not congruent. Same can be applied to that of a rectangle as well, it's diagonals aren't congruent, even if they appear perpendicular.
On the other hand, the diagonals of a rhombus is both perpendicular, and at the same time congruent. And thus, that's our answer
