Which one of the following instrument is used for locating submerged objects in the ocean?

Which one of the following statements is not true for a flute, a musical instrument?

Which one of the following units is used for measurement of noise pollution?

Which one of the following statements is true for sound waves propagating in air?

Which one among the following is true for the speed of sound in a given medium?

Which of the following is not a musical instrument that produces sound by vibrating a string?