Answer:
d. wavelength/2.
Explanation:
The circular motion of water molecules extends from regions of shallow water to deep water. It ranges from a depth, H < L/20 for shallow water to a depth of H > L/2 for deep water where L is the wavelength of the wave.
For depths greater than L/2,the circular motion is not affected by the wave energy. So, the maximum depth for the circular motion is L/2 = wavelength/2.
