- Statement I: When a wave travels from one medium to another, its frequency remains constant (determined by the source), but its speed and wavelength change. Therefore, Statement I is false. - Statement II: The frequency of a wave, including ultrasound, is determined by the source of the wave and does not change when it passes from one medium to another. The speed and wavelength change because speed = frequency x wavelength (v = fλ). If speed changes and frequency is constant, wavelength must change. Statement II is true. - Statement III: This statement claims both frequency and speed change. As established, frequency remains constant. Therefore, Statement III is false. - Statement IV: Echocardiography is a medical imaging technique that uses ultrasound waves to create images of the heart. This statement is true.