Rhombus.
Square.
Most quadrilaterals do not.
i think its a trapezoid...
The diagonals are perpendicular, but not necessarily congruent.
No. If the diagonals of a parallelogram are congruent then it must be a rectangle (or square).
A quadrilateral with four congruent sides and uncongruent diagonals is a Rhombus. See related link for a picture
congruent
The quadrilateral that must have diagonals that are congruent and perpendicular is the square. This is because its diagonals form a right angle at its center.
It is a square.
Rhombus.
Square.
square
A square
Most quadrilaterals do not.
A rhombus
A square would fit the given description.