The frequency of oscillation of the floating leaf is twice the frequency of the passing water wave since the leaf completes two cycles while the wave completes one wavelength. Therefore, the frequency of the wave is 2 Hz (cycles per second).

The formula relating wave speed, frequency, and wavelength is:
Wave speed = Frequency × Wavelength

Given that the wavelength is 10 m and the frequency is 2 Hz, the wave speed is:
Wave speed = 2 Hz × 10 m = 20 m/s