The human auditory system is capable of detecting sound waves within a specific frequency range, typically defined as 20 Hz to 20,000 Hz. Frequencies below 20 Hz are classified as infrasound and are generally not perceived as sound by humans, although they may be felt as vibrations at very high intensities.

Pitch is the human perception of the frequency of a sound wave. A higher frequency corresponds to a higher pitch, while a lower frequency corresponds to a lower pitch. While intensity and amplitude relate to the loudness of the sound, frequency is the specific physical parameter that dictates the pitch perceived by the human ear.

The statement that sound velocity decreases with humidity is incorrect. In reality, the velocity of sound increases as humidity increases because water vapor is less dense than dry air. Since the speed of sound is inversely proportional to the square root of the density of the medium, lower density results in a higher speed of sound.

A silent dog whistle operates in the ultrasonic range, which is above the human hearing threshold of approximately 20,000 Hz. Dogs have a much higher upper limit of hearing than humans, allowing them to perceive these high-frequency sounds that are inaudible to us. The range of 20,000 Hz to 25,000 Hz falls within the ultrasonic spectrum detectable by canine ears.

The human ear's sensitivity is highly dependent on frequency. We are most sensitive to sounds in the range of 2 kHz to 5 kHz and significantly less sensitive to very low or very high frequencies, making statement B incorrect.

To hear a distinct echo, the reflected sound must reach the ear at least 0.1 seconds after the original sound. Given the speed of sound is roughly 330 m/s, the total distance traveled by the sound is 33 meters. Since the sound must travel to the wall and back, the minimum distance to the reflecting surface is half of that, which is 16.5 meters.

The human ear requires a time interval of at least 0.1 seconds to distinguish between the original sound and its reflection. Given the speed of sound in air is approximately 340 m/s, the total distance traveled by the sound wave must be at least 34 meters (340 m/s * 0.1 s) to create a distinct echo.

Statement A is generally accepted as a standard value for seawater. Statement B is incorrect because the speed of sound in ethanol is approximately 1200 m/s, not 1200 km/s. A speed of 1200 km/s would be physically impossible for sound in a liquid medium, as it exceeds the speed of sound in most solids.

The speed of sound in air at room temperature is approximately 340 m/s, and at 0°C it is approximately 331 m/s. Therefore, 330 m/s is the standard approximation used in most introductory physics problems to represent the speed of sound in air.

The speed of sound in air is dependent on the density and humidity of the medium. Moist air is less dense than dry air because water vapor has a lower molecular weight than nitrogen and oxygen. Consequently, sound waves propagate at a higher velocity through humid air, allowing the sound to travel more efficiently and be heard over longer distances.