Concept:Rarefaction is a region of a longitudinal wave where particles are spread apart, causing low density and low pressure.
Explanation:Sound propagates in air as a longitudinal wave.
It consists of alternating regions called compressions and rarefactions.
In a compression, particles are close together, so density is maximum and pressure is high.
In a rarefaction, particles are far apart, so density is minimum and pressure is low.
Therefore, rarefaction is the region where density is minimum.
Option A, "particles are very close", describes a compression, not a rarefaction.
Option C, "pressure is high", also describes a compression.
Option D, "wavelength becomes zero", is incorrect because a wave must have a finite wavelength to propagate; zero wavelength means no wave exists.
The wavelength
λ is the distance between two consecutive compressions or two consecutive rarefactions.
Sound waves require a material medium and cannot travel through a vacuum.
Thus, the region of rarefaction corresponds to minimum density.
Answer:Option B — density is minimum.