Two children are at the opposite ends of an iron pipe. One strikes an end of the pipe with a stone. Which of the following statements is correct ?

The speed of sound is determined by the properties of the medium through which it travels. Sound is a mechanical wave that propagates via the vibration of molecules; consequently, it travels faster in media where molecules are more tightly bonded and can return to their resting positions quickly. In general, sound waves travel fastest in solids, followed by liquids, and slowest in gases [1]. Specifically, the speed of sound in iron (a solid) is approximately 5,180 m/s, whereas in air (a gas), it is only about 331–343 m/s [1]. Because the speed in iron is significantly higher than in air, the sound wave traveling through the iron pipe will reach the other end much faster than the wave traveling through the air inside or around the pipe. Therefore, the time taken by the sound waves in air is more than that taken in iron.

Sources

1. [1] https://www.nasa.gov/wp-content/uploads/2018/07/speed_of_sound_9-12.pdf