Explanation

Sound is propagated in the form of longitudinal waves. When sound travels from one medium to another medium the wavelength and velocity remains changed and the frequency remains unchanged.The velocity of sound in the given medium is obtained by v=nW, where “n” is the frequency of sound and “W” is its wavelength in that medium. Velocity of sound is directly proportional to the wavelength.Thus, if the velocity of sound wave doubles when travelled from one medium to another medium then its wavelength also doubles.The frequency of sound depends on the source of the sound, not the medium of propagation .Hence the frequency does not change when travelled from air to water.