Identify the correct statement from among the following:

Three independent properties describe a sound wave. Pitch is the perceived highness or lowness of a sound and is governed by the frequency of vibration: a higher frequency gives a higher pitch, and a lower frequency gives a lower pitch. Loudness is the perceived intensity of a sound and is governed by the amplitude of vibration, not by frequency. Sound itself is a mechanical wave, so it needs a material medium — solid, liquid, or gas — whose particles can vibrate and pass the disturbance along; with no particles present, a vacuum cannot carry a mechanical wave.

Applying these principles to the four statements given:

• The claim that a lower vibration frequency gives a higher pitch reverses the pitch-frequency relationship — pitch rises with frequency, it does not fall as frequency rises.

• The claim that loudness is fixed by the frequency of vibration swaps the controlling variable — loudness tracks amplitude, while frequency instead governs pitch.

• The claim that sound cannot travel through vacuum matches the medium-dependence of a mechanical wave exactly, since propagation needs particles to vibrate.

• The claim that pitch is fixed by amplitude also swaps the controlling variable — pitch tracks frequency, while amplitude instead governs loudness.

As a check, notice amplitude and frequency are independent wave parameters that each control a different perceived quality — one governs how loud a sound seems, the other how high or low it seems — while medium-dependence is a separate propagation requirement altogether, so only the statement about propagation through vacuum holds up under both checks.

Hence, the statement that sound cannot travel through vacuum is the correct one.