The correct answer is $\boxed{\text{B) 0.50 cm}}$.
The center of mass (CM) of a circular plate is located at its geometric center. When a circular plate with a diameter of 6 cm is cut out of a circular plate with a diameter of 6 cm, the CM of the remainder shifts towards the center of the cut-out circle. The radius of the cut-out circle is 3 cm, so the diameter of the cut-out circle is 6 cm. The distance between the CM of the original circle and the CM of the cut-out circle is 3 cm. Therefore, the CM of the remainder shifts 0.5 cm towards the center of the cut-out circle.
Option A is incorrect because the CM of the remainder shifts 0.5 cm, not 0.25 cm.
Option C is incorrect because the CM of the remainder shifts 0.5 cm, not 0.75 cm.
Option D is incorrect because the CM of the remainder shifts 0.5 cm, not 1 cm.