The loudness of a sound refers to how strong or intense the sound is perceived by the human ear. It is influenced by several factors.

Option 1: The velocity of sound waves in the medium is not directly related to the loudness of a sound. The velocity of sound waves determines how quickly the sound travels through a medium, but it does not affect how loud or soft the sound is perceived to be.

Option 2: The amplitude of the sound waves does affect the loudness of a sound. The amplitude refers to the maximum displacement of the particles in a medium caused by the sound wave. Greater amplitude means the particles are displaced more, resulting in a louder sound.

Option 3: The frequency of the sound waves also plays a role in determining the loudness of a sound. Frequency refers to the number of vibrations (or cycles) per second in a sound wave. Generally, higher frequency sounds are perceived as being louder than lower frequency sounds, assuming the amplitudes are the same.

Option 4: The combination of frequency and velocity of sound waves is not directly related to the loudness of a sound. While both factors affect the characteristics of a sound wave, they are not the primary determinants of loudness.

Overall, the correct answer is option