What is the biconditional statement of the following conditional statement?

"If a polygon has six sides, then it is a hexagon."

If a polygon does not have six sides, then it is a not hexagon.
A polygon has six sides if and only if it is a hexagon.
If a polygon is a hexagon, then it has six sides.
If a polygon is not a hexagon, then it is does not have six sides.

A polygon has six sides if and only if it is a hexagon.