Which of the following statements is NOT a property of a parallelogram?

A parallelogram is a four-sided shape whose two pairs of opposite sides are parallel. From that one fact, three other properties follow: opposite sides are equal in length (congruent), opposite angles are equal, and the diagonals cut each other in half.

What a parallelogram does NOT need is right angles. Its angles only have to satisfy this rule: two angles next to each other add up to 180°. So a parallelogram can have angles of 60° and 120°, like a leaning (slanted) shape. Nothing forces them to be 90° each.

So the statement that all angles are right angles is the odd one out. When a parallelogram does happen to have four right angles, it stops being just any parallelogram and becomes a special one called a rectangle. Every rectangle is a parallelogram, but not every parallelogram is a rectangle, so that property cannot be listed as a property of parallelograms in general.