Loudness of a sound wave varies directly with the vibrating body’s(a) Intensity(b) Frequency(c) Amplitude(d) Quality

The loudness of a sound wave varies directly with the vibrating body's amplitude. So, the correct answer is (c) Amplitude.

Here's why:

Sound is a type of energy made by vibrations. When any object vibrates, it causes movement in the air particles. These particles bump into the particles close to them, which makes them vibrate too causing them to bump into more air particles. This movement, called sound waves, keeps going until they run out of energy.

The amplitude of a sound wave determines its volume. When the amplitude is high, the sound is loud; when the amplitude is low, the sound is soft. The frequency of a sound wave, on the other hand, affects the pitch of the sound. High frequency sounds are high-pitched (like a whistle), while low frequency sounds are low-pitched (like a drum).

Intensity is the amount of energy a sound wave carries per second through a unit area and it also affects the loudness of a sound, but it's not the vibrating body's property, it's the sound wave's property.

Quality, or timbre, is the characteristic of a sound that distinguishes different types of sound production, such as voices or musical instruments. It does not affect the loudness of the sound.