What happens during "destructive interference" of waves?

During destructive interference of waves, two or more waves meet in such a way that their crests and troughs are aligned oppositely. When this occurs, the amplitude of the resultant wave is reduced or can even become zero if the waves are perfectly out of phase—meaning the crest of one wave aligns with the trough of another. This cancellation effect results in a lower overall intensity or amplitude of the combined wave, demonstrating how the superposition principle works in wave physics.

In contrast, the other options describe different phenomena. For example, when wave amplitudes double, that describes constructive interference, where waves are in phase and combine to create a larger wave. Merging perfectly also relates to constructive interference, as it implies alignment that enhances amplitude. The speed of wave propagation typically does not change with interference; rather, it's determined by the medium through which the waves travel. Therefore, the correct answer highlights the fundamental nature of destructive interference in wave behavior.