The blank is determined by the medium, not the sound source.

• A. Wavelength
• B. Speed of sound
• C. Frequency
• D. Amplitude

Answer: (B)

The main idea is that how fast a sound wave moves depends on the medium itself, not on how the sound is produced. The speed of sound is set by the medium’s properties—its stiffness (how quickly particles transmit a disturbance) and its density (how heavy the particles are). A denser or less stiff medium slows the wave, while a stiffer or less dense medium speeds it up. Because of this, the same vibrating source can emit waves with a fixed frequency, but the waves will travel at different speeds in different media, and their wavelengths will adjust accordingly via the relationship v = fλ.

Amplitude describes how strong the wave is, which is influenced by the source strength and how the medium attenuates the wave, not by the intrinsic speed of propagation. Wavelength isn’t determined solely by the medium either, since it also depends on the frequency set by the source. So the statement points to the speed of sound as the property governed by the medium.