All of the above are the measures to control noise pollution.

Noise pollution causes partial hearing impairment. Presence of excess sound in environment is termed as noise pollution. Air conditioners contribute to noise pollution because of their constant hum.

If a sound is high-pitched and feeble, the sound wave has high frequency and low amplitude. 

In Doppler effect, when the sound source moves away from the receiver at rest, the frequency of sound that is heard decreases.

Doppler effect is applicable to both sound and light waves.

A group of sound waves having high pitch is known as treble.

The normal frequency range of hearing in a bat is 40 - 120, 000 Hz.

Presence of excessive noise in our surroundings may cause many health related problems like lack of sleep, hypertension, anxiety, etc. but it is not one of the many causes of skin cancer.

Frequency determines the pitch of a sound.

Echoes are heard due to successive or multiple reflections.

Sound is produced when a body vibrates in a medium.

Sound is a mechanical wave and needs a material medium like air, water, steel, etc. for its propagation, i.e. it cannot travel through vacuum. Thus, Neil Armstrong would not have been able to hear any sound except for his communication with mission control through his headset when he was walking on the surface of Moon as Moon has no atmosphere.

The phenomenon of reflection of sound is involved in the use of megaphone, stethoscope used by doctors and in a theatre with curved ceiling. Two persons talking to each other in a small room do not employ reflection of sound.

Frequencies higher than 20 kHz, i.e. 20,000 Hz are associated with ultrasonic sounds or ultrasounds.

Ultrasonic waves have the tendency to travel in a straight line and have high penetration power. Thus, ultrasonic waves are preferred for industrial applications.