A Christmas Ornament Made from a Thin Hollow Glass Sphere

A Christmas ornament made from a thin hollow glass sphere hangs from a small hook at its surface. It is observed to oscillate with a frequency of 2.50 Hz. What is the radius of the ornament? The moment of inertia of a hollow sphere of mass M and radius R about a point on its edge is 5MR²/3.

A) 1.84 cm
B) 3.68 cm
C) 2.39 cm
D) 3.98 cm
E) 4.69 cm