(I) Radius of spherical ball r = 28/2 = 14 cm
Volume of water displaced by spherical ball = 4/3πr³
= 4/3 × 22/7 × 14 × 14 × 14 × = 4/3 × 22 × 2 × 14 × 14 = 11498(2/3) cm³
Hence, the volume of water displaced by spherical ball is 11498(2/3) cm³.

(II) Radius of spherical ball r = 0.21/2 = 0.105 m
Volume of water displaced by spherical ball = 4/3πr³
= 4/3 × 22/7 × 0.105 × 0.105 × 0.105 = 4 × 22 × 0.005 × 0.63 × 0.63 = 0.004861 m³
Hence, the volume of water displaced by spherical ball is 0.004861 m³.