Wavelength in Longitudinal Waves Steps:

• Recall that longitudinal waves propagate with compressions and rarefactions along the direction of travel.
• Identify the longitudinal waveform in the diagram, typically shown as a series of dense and sparse regions.
• Measure wavelength as the distance between two consecutive compressions or rarefactions.
• Locate the arrow that spans this distance on the longitudinal wave.

Why A is correct:

• Arrow A marks the distance between consecutive compressions, matching the definition of wavelength as the repeat distance in longitudinal waves.

Why the others are wrong:

• B points to amplitude on the transverse wave, not wavelength.
• C indicates a single compression, which is not the full wavelength.
• D spans multiple wavelengths on the transverse wave, misapplying to longitudinal.

Final answer: A