Sound is a mechanical wave that requires a material medium (solid, liquid, or gas) to travel, as it relies on the vibration of particles to transfer energy. A vacuum contains no particles, therefore sound waves cannot propagate through it.

According to the ideal gas law, the speed of sound in a gas is given by v = sqrt(γRT/M). Since the density and pressure change proportionally with volume at a constant temperature, the ratio of pressure to density remains constant. Thus, pressure does not independently affect the speed of sound.

The speed of sound is dependent on the mechanical properties of the medium. Solids are characterized by strong intermolecular forces and high stiffness, which facilitate rapid wave propagation. Gases have much weaker intermolecular forces and lower density, resulting in significantly slower wave propagation. Therefore, as sound moves from a solid to a gas, its speed decreases substantially due to the change in the medium's elastic properties.

Statement I is correct because pitch is the human perception of frequency. Statement II is correct because loudness is the human perception of amplitude. However, these are independent physical characteristics of sound waves; the amplitude does not cause the frequency, nor does frequency cause the amplitude. Therefore, while both statements are factually accurate, the second does not explain the first.

Noise is defined as an irregular, non-periodic, or unpleasant sound that lacks a consistent pitch or rhythm. Unlike music, which is characterized by harmonious frequencies and pleasing patterns, noise is typically perceived as jarring or irritating to the human auditory system.

Sound travels significantly faster in solids than in gases due to the higher elasticity and density of solid materials. While the exact ratio depends on the specific material and gas, it is generally accepted in many introductory physics contexts that the speed of sound in solids is approximately 15 times greater than in air.

Acoustic treatment involves using materials that absorb sound energy rather than reflecting it. Soft and porous materials, such as foam or acoustic panels, are effective at converting sound energy into heat through friction within the pores, thereby reducing echoes and reverberation. This practice is essential in architectural acoustics to improve sound quality within a space.

The speed of sound in air increases with humidity because water vapor is less dense than dry air. Since the speed of sound is inversely proportional to the square root of density, lower density leads to higher speed. Statement C is incorrect because it claims speed decreases with humidity.

Infrasonic sound refers to sound waves with frequencies below the lower threshold of human hearing, which is approximately 20 Hz. Any sound wave with a frequency lower than this limit is categorized as infrasonic, meaning it cannot be perceived by the human ear, although it may be detected by certain animals or specialized equipment.

Glass wool is highly effective as a sound absorber because its porous, fibrous structure traps sound waves and converts their mechanical energy into heat through friction. Unlike dense materials like steel or stone, which reflect sound, the low-density, flexible nature of glass wool prevents the transmission of vibrations, making it ideal for acoustic insulation in walls.