The distance between two consecutive compressions.
Explanation
Sound waves are longitudinal mechanical waves that propagate through a medium by creating alternating regions of high pressure (compressions) and low pressure (rarefactions). The characteristics of these waves are defined by parameters such as wavelength, frequency, amplitude, and speed.
Analysis of the Options:
- The distance between a compression and the adjacent rarefaction. is incorrect: The distance between a compression and the adjacent rarefaction represents half of a wavelength ($\lambda/2$).
- The distance between two consecutive compressions. is correct: The wavelength ($\lambda$) is defined as the distance between two consecutive compressions or two consecutive rarefactions. It represents the minimum distance in which the sound wave repeats itself.
- The distance travelled by the wave in one second. is incorrect: The distance travelled by the wave in one second is defined as the wave speed or velocity ($v$).
- The maximum displacement of the particle from its mean position. is incorrect: The maximum displacement of the particle from its mean position is defined as the amplitude ($A$) of the wave, which determines the loudness of the sound.
Key Takeaway: Wavelength is the spatial period of a wave, measured as the distance between two consecutive points in the same phase of oscillation (e.g., compression to compression).