Given:

The given sentence is:

Two circles are concentric circles if and only if they have congruent radii.

Calculation:

The definition of concentric circle states that these are the coplanar circles having same center.

Two circles are congruent circles if and only if they have congruent radii.

Hence, the given sentence is false.

The given sentence is:

Two circles are concentric circles if and only if they have congruent radii.

Calculation:

The definition of concentric circle states that these are the coplanar circles having same center.

Two circles are congruent circles if and only if they have congruent radii.

Hence, the given sentence is false.