The correct increasing order of speed of sound in the given materials as follows: Vacuum < Air < Water < Metal Sound requires the medium to travel. As the medium become denser, the speed increases.

Statement 1 is correct. Mach number is a dimensionless quantity representing the ratio of speed of the object to that of the speed of the sound. Statement 2 is also correct. Tinnitus is a resultant condition of noise pollution. In this, patient perceives the ringing noise in his/her ears.

Statement 1 is correct. Supersonic Jet, flying at stratosphere heights, causes a major disturbance in the ozone levels. Statement 2 is incorrect. Ultrasonic (frequency greater than the upper limit of the human hearing range) sound waves are used to clean clothes and fine machinery parts.

Statement 1 is incorrect. The velocity of sound in deep water is more than the velocity in shallow water. Statement 2 is also correct. Ultrasonic waves are used in sonography.

Statement 1 is incorrect. The walls of the halls built for musical concert should absorb the sound. If not, sound is reflected from walls, ceilings or floors which disturbs the sound from an orchestra or a speaker which reaches the audience. Statement 2 is correct. Scanners producing ultrasonic waves are used to locate the tumors in a tissue.

Statement 1 is correct. Doppler principle is the apparent change in frequency (and wavelength) of a wave that is perceived by an observer with respect to the change in the distance between the observer and the source. This principle is observed by both light and sound waves. Statement 2 is also correct. Ear pinna receives the sound from external environment. The pinna captures sounds in the environment and increases the loudness of those pitches that make it easier to understand speech.

Sound requires medium for its propagation and is there no medium between sun and earth, hence, sound cannot reach the earth. Heat and light are non- mechanical waves and do not require medium for propagation. When sound travels from one medium to another, the frequency of sound waves does not change. The frequency of sound depends upon the source of sound, not the medium of propagation.

1. Yes, whenever a body vibrates in a medium, sound will produce.
   1. The speed of sound depends on the medium. (Air < Liquid < Solid)
   2. Sound is a form of energy because energy always carried sound waves.
   3. The speed of sound is independent of pressure.

Statement 1 is incorrect. Dolphins detect their enemy and obstacles by emitting the ultrasonic waves and hearing their echo. Solution 2 is correct. The tuning of radio and TV receivers is based on resonance. Radio and TV receivers have electronic circuits which produce vibrations of the different frequencies.

Statement 1 is correct. When a guitar is played, the artist forces the strings of the guitar to execute forced vibrations. Statement 2 is incorrect. Loudness of a sound depends on the density of medium. More the density of medium, more is the loudness.

Statement 1 is incorrect. Infrasonic sound waves are utilised for monitoring earthquakes, charting rock and petroleum formation below the earth. Statement 2 is also incorrect. Above 120 dB, the sound produced is regarded as noise pollution. The audible range of humans is 0dB - 120dB

The sound requires the medium to propagate. Sound travels with higher speed in water as compared to that in dry air.

1. Pitch - (ii) Sensation perceived by the listener
   1. Echo - (i) Hearing of sound after reflection
   2. Doppler effect - (iv) Change in frequency of sound with respect to body position
   3. Quality (Timbre) - (iii) Difference in two sounds of the same loudness

Statement 1 is correct. The US Department of Defense (DOD) has acoustic weapons that use sound to injure, incapacitate or kill an opponent. Statement 2 is also correct. The intensity of sound increases at night due to increase in density of air.

Statement 1 is correct. Larynx is responsible for the voice in humans. Therefore it is also called voicebox. Statement 2 is also correct. The sound falls on the diaphragm of the microphone and produces vibrations of high frequency.