Final answer:
When a sound wave moves from air to water, it speeds up due to the increased density of water compared to air. The frequency of the sound wave remains constant, leading to a longer wavelength in the water.
Step-by-step explanation:
When a sound wave moves from air into water,option 2) it speeds up because water is denser than air, meaning the particles are closer together. As a result, sound waves can travel faster through water than in air. Although the speed of the sound wave increases, the frequency remains the same; this leads to a change in wavelength. In the case of sound, the relationship between speed (u), frequency (f), and wavelength (λ) is given by u = fλ, so if the speed increases and the frequency stays constant, the wavelength must increase as well.