Which of the following statements doesn't guarantee that the figure is a square?

A square is a parallelogram whose all sides are equal and all angles are right-angled. 

But a parallelogram with diagonals that are perpendicular can be a rhombus whose all sides are equal but whose angles are not right-angled. So not every rhombus is a square.

Therefore, the property 'a parallelogram with diagonals that are perpendicular' doesn't guarantee that the figure is a square.