Which of the following is NOT a characteristic of sound wave?

The correct answer is option 2. Nature.

Out of the following options, Nature is NOT a characteristic of a sound wave.

Velocity refers to the speed at which sound travels through a medium.

Wavelength is the distance between repeated features of a wave, including sound waves.

Amplitude represents the maximum displacement of the medium from its rest position in a sound wave, which determines the loudness of the sound.

Nature, in this context, isn't a specific property of a sound wave itself. Sound waves are a type of mechanical wave characterized by the properties mentioned above.