Answer:

• Opposite sides are parallel and congruent.
• Opposite angles are congruent.
• Adjacent angles are supplementary.
• Diagonals bisect each other and each diagonal divides the parallelogram into two congruent triangles.
• If one of the angles of a parallelogram is a right angle then all other angles are right and it becomes a rectangle.

2.

• both pairs of opposite angles of a quadrilateral are congruent, then it's a parallelogram (converse of a property). If the diagonals of a quadrilateral bisect each other, then it's a parallelogram (converse of a property).