The correct answer is option 'D', oscillatory.

Explanation:
When a sound wave passes through a medium, the particles of the medium vibrate or oscillate in a specific pattern. This motion of the particles is referred to as oscillatory motion.

Sound waves are mechanical waves, which means they require a medium to propagate. In the case of sound waves, the medium can be a solid, liquid, or gas. When a sound wave is produced, it creates a disturbance in the particles of the medium. This disturbance is transmitted from one particle to the next, causing a chain reaction of oscillations.

Key Points:
1. Sound waves are generated by a vibrating source, such as a tuning fork or vocal cords.
2. The vibrating source creates compressions and rarefactions in the medium, which are regions of high and low pressure respectively.
3. As the sound wave propagates through the medium, the particles in the compressions are pushed closer together, while the particles in the rarefactions are spread out.
4. The particles in the medium do not move in a straight line as the wave passes through them. Instead, they vibrate or oscillate about their equilibrium positions.
5. The oscillatory motion of the particles is perpendicular to the direction of propagation of the sound wave.
6. The amplitude of the particle's motion determines the loudness of the sound, while the frequency of the motion determines the pitch.
7. The particles of the medium do not move forward with the wave. Instead, they oscillate back and forth about their equilibrium positions.
8. This oscillatory motion is responsible for the transfer of energy from one particle to the next, allowing the sound wave to propagate through the medium.

In conclusion, the motion of the particles of a medium when a sound wave passes through it is oscillatory. The particles vibrate or oscillate about their equilibrium positions, transmitting the energy of the wave from one particle to the next.