When sound waves travel from one medium to another, which of the following physical quantities does not alter?
A) Amplitude
B) Velocity
C) Frequency
D) Intensity

Hint: The sound travels as longitudinal waves. If the sound moves from medium to medium, its wavelength and velocity changes.

Complete step by step solution:
Sound is a mechanical wave formed by an entity that vibrates. The entity vibrations place objects in vibration motions in the surrounding medium, transferring energy through the medium. The vibration of the particles is defined as longitudinal for a sound wave that passes through air. Longitudinal waves are waves in which the acceleration of each of the medium's particles is parallel to energy transfer. When the slinky is spread horizontally and the first slinky bands are vibrated horizontally, a longitudinal wave is produced in a slinky position.

In the form of longitudinal waves, sound spreads. If the sound is transported from medium to medium, the speed and longitude can change. The sound velocity in a given medium is achieved by the equation $v = f\lambda$ where $f$ is the sound frequency and $\lambda $ in that medium is its wavelength.

The sound speed is directly commensurate with the wavelength. So if the sound velocity doubles, the wavelength doubles, whether it passes from medium to media. The sound frequency depends on the sound source and not the propagation medium. It's not evolving, therefore.

Hence, the correct option is (C) that is frequency does not change going from one medium to another.

Note: The sound's wavelength is not specifically sensed. Subtle evidence can be seen in the contrast between the scale and pitch of musical instruments. The common sounds of small instruments like a piccolo are high-pitch, while large instruments like a tuba normally create low-pitch sounds. High wavelength means short wavelength and is closely connected to the wavelengths of the sound created by the musical instrument. A small tool produces sounds with short wavelengths. A large instrument emits wavelength sounds, like claims.