Concept:Loudness of sound is directly determined by the amplitude of the sound wave. Greater amplitude means louder sound.Explanation:Amplitude is the height of the wave from its rest position. Larger amplitude carries more energy, making the sound louder. Loudness is measured in decibels (dB). For example, a whisper has small amplitude, while a shout has large amplitude. Other properties like wavelength, pitch, and frequency do not affect loudness. Wavelength is the distance between wave peaks; it affects the type of sound but not loudness. Pitch depends on frequency – higher frequency gives higher pitch. Frequency is cycles per second (Hz); it influences pitch only. Decibel scale: 0 dB is the threshold of hearing; prolonged exposure above 85 dB can damage hearing.Answer:C. Amplitude