Answer:
2. Sound
Step-by-step explanation:
There are two types of waves:
- Transverse waves: in a transverse wave, the vibration occurs in a direction perpendicular to the direction of motion of the wave. Such wave is characterized by the presence of crests (point of maximum positive displacement) and troughs (points of maximum negative displacement). Examples of transverse waves are electromagnetic waves.
- Longitudinal waves: in a longitudinal wave, the vibration occurs in a direction parallel to the direction of motion of the wave. Such wave is characterized bu the presence of compressions (areas where the density of particles is maximum) and rarefactions (areas where the density of particles is minimum). Examples of longitudinal waves are sound waves.
In this list, only sound waves and elastic waves are longitudinal waves, so they are the only waves in the list having compressions (light is part of electromagnetic waves, which are transverse waves, so they do not have compressions).
However, the sentence is:
"...energy wave is transferred through a substance as a series of compressions."
This is more appropriate to describe sound waves, which are pressure waves that transmit energy through a medium through a series of compressions and rarefactions.
(Elastic waves instead are those in a string, which has a limited displacement, so it does not propagate through a substance as the sound waves do.)
So, the correct answer is
2. sound